Sound too good to be true? Well then, you'll be floored by this. You can do 85% of your electrical system in the comfort of your own home, sitting or standing, what ever your workspace is best suited for. Here is how you do it...

Take your notebook and on the first page make a list of everything in your airplane that has a wire going to it. List each radio, indicator, interior or exterior light, gear warning system, everything. If you have cabin lights, list them separately so you don't overlook one. Nothing is more frustrating than to have wired your airplane and realize that the wire for the aft cabin light was left out! You will be referring back to this list often so don't forget anything. Then, let your list set for a day or so. Go back and check it for any omissions.

Next, draw a line under your list. Virtually every pilot I have known who has owned an airplane has added something to his plane by the third or fourth year of ownership. This is our "Wish List".( If you are building your plane to attempt a world class speed record you may omit this step.)

If you've ever had the opportunity to stick your head up under the panel of an older airplane, you know first hand how bad an electrical harness can get. Its often called a 'rats nest'. It gets this way, a lot of times, because one system after another was added to, and on top of, the original harness. The goal here is to pre-wire your aircraft for realistic 'wish list' items that will be installed in the next few years. What this also means is that when you do get around to adding your 'wishes', you won't have to tear your airplane apart to route wires and coax. Just connect the proper connectors to your stowed harness and mount the hardware. The argument that current radio equipment and electrical systems will be different in a few years might be true, but the current generation of radios such as the King KX 155 and the NARCO MK-12 D&E have been around for most of the last 20 years. Same goes true for such systems as the Whelen strobe lights. In any case, you know you will need the basics such as power, ground, dimmer, and in some cases, audio wires. You are the one to decide whether or not you want to do this step. If it is done with reasonable optimism, you'll be glad you did it.

Once you have determined what is going to be in the airplane, you need to make sure you have the proper wiring diagrams, or interconnects, for your specific systems. There are numerous manuals for basic aircraft electrical systems such as Nav/Position Lights, Landing and Taxi lights, and so forth. Getting diagrams for your radios and such can be a little harder. Most new radio equipment will come with wiring diagrams. If not, contact the manufacturer of the radio system you are going to use. Tell them that you wish to prewire your plane for that system and most manufacturers will help you out.

Now, you have established what is going in your plane and you have the proper wiring diagrams to do it. Most diagrams will specify the proper wire sizes needed to do the job. However, if they do not, there is one source you can use to determine the wire size you need for anything, provided you know two things:

(1) How far am I going to run the wire?, and

(2) How much current (amps) does the circuit use?

This one source is also the best $15.00 you will ever spend on your aircraft. That source is from the Government Printing Office (GPO) and is called AC 43.13-1A and -2A. It is the aircraft bible of an airframe and powerplant mechanic (A&P).

What you have accomplished so far is about 20% of wiring an airplane. Armed with the information you have generated yourself, you are ready to get down to business. Please, stay seated unless you need to refresh your drink!

Draw a likeness of your airplane, canard or conventional. With your 'checklist' and your diagrams, draw in the 'wires' for your left wing. (This whole process may take more than one piece of paper.) If you have a composite or wood and fabric airplane, remember that you will need to run at least one ground wire out for lights, pitot heat, whatever. A separate ground should be run for each item on your list. For whatever reason, one wire providing ground for an entire wing could break and all systems would quit working. If you elect to run just one ground wire, remember to size it for the total current (amps) of all the systems that will be grounded to it.

Once you have determined what wires are needed for the left wing, do the right wing, the aft cabin or engine/cabin (in the case of a 'pusher') and forward of the instrument panel. As soon as it is convenient, take a tape measure and measure the route in which these four separate harness need to go, noting distances between bends, such as where the harness might go down to the floor from the instrument panel to where it bends to go aft, and where any given system wire has to 'break out', such as a pitot heat in a wing harness. Whatever you do, measure 'comfortably'. Remember, we don't want these harnesses bow string tight. For reasons that will be clear when you go to install your harness, take the measured distance and add 10%. Trust me on this one. It is easier to cut off a foot than to add 2". (And butt slices in a new electrical system look.... well, just do it right the first time!)

You are now 60 % complete with your electrical system! You have done two major things so far. First, you have established the ability to make what is called a wire schedule. You don't have to guess how much wire and what sizes you need to buy. You know exactly what sizes and you can total the lengths so you don't have to buy 300 feet too much ( or 100 feet too little!). Contrary to popular belief, one size does not fit all! Second, and most important of all, your have already wired your plane up in your head! With all of this accomplished in the comfort of your own home!!! The only thing left to do is the mechanics.

You can still do the next 25% of your electrical system in an environment of your choice. Once you have purchased your wire and your RG 58 A/U coax (I'll discuss materials at the end of the article), find a clean workbench about 8 feet long and wide enough to reach across, and several "C" clamps and/or nails.

What you are about to do is prewire and secure (lace or ty-wrap) your four harnesses (left, right, fore, and aft). At one corner of the bench, attach a "C" clamp. For harnesses over 8 feet, secure a second "C" clamp at the other end of the bench. If your harness is over 16 feet, attach a third "C" clamp near your first clamp. For a 24 foot harness, attach a fourth "C" clamp near your second clamp, and so forth. When you go to lay your harness out you will run (zig-zag) the wires between clamps on the opposite ends of the table. If, for example, we need two 18 AWG wires for our Nav light (1-18 feet long to our switch, 1-22 feet long to our ground buss), two 16 AWG wires for our pitot heat(1-14 feet to our switch, 1-18 feet to the ground buss), and three 22 AWG wires for our gear position switches (all 9 feet to your warning lights), in our left wing, this is how we make the harness...

The first clamp we put on the bench represents the end of the wing were the Nav light is. Secure two 18 AWG wires to the clamp, 1-18' long and the other 1-22' long. Run (zigzag) the wires around the second and third clamp and tape the ends to the top of the table. (If you can visualize this, you can see how easy this is going to be!) Since our Nav light and Pitot switches are located in the same area on the instrument panel, you start your pitot heat switch wire (16 AWG -14' long) were your Nav light switch wire is taped to the table and run it with the Nav light wire toward "the end of the wing". The wire you just put in the harness should go around the third clamp , back around the second clamp toward the first "C" Clamp for those who haven't quite got the picture yet. The ground for the pitot goes to the same place as the Nav light ground so tape it down at the same place where the Nav light ground is taped down. This wire should now be routed along with the other wires in the bundle.

By referencing where grounds, switches, and harness ends are, you can make your own harnesses up on the bench. This is a lot simpler than laying on your side or your back trying to route one wire at a time. When you have finished laying in all the wires that you need, you can start securing your harness. This can be accomplished in three ways...

First, if you are using conduit in your plane (Nylon tubing, Aluminium, fibreglass, etc.) all you need is masking tape. Put two wraps of tape at the ends, three wraps at key breakout points (i.e. where the pitot heat wires breakout from the main harness to the pitot heat), and two wraps at approx. 1 foot intervals. As you pull, or push, your harness into the conduit in your aircraft, remove the tape. The whole idea behind conduit is for easy installation of, or removal of, one or more wires. If you leave the tape on and you need to remove one wire, guess what? Second, you can use ty-wraps. These are readily available in plastic or nylon. Get the nylon type. How can you be sure what type you have? If you bend the flat part of the ty-wrap over 180 degrees, the plastic will leave a white or discoloured mark. A nylon tywrap will remain unchanged in colour.

NOTE: If you have coax in the harness that you are securing, DO NOT deform the outer insulation of the coax! You will create a problem that will wait to happen. By the same token, DO NOT bend a sharp radius in coax. If you have excess coax do not double it up in the harness with tight bends at the ends. Make a loop if at all possible. Over long periods of time, the centre conductor can "migrate" to the inside of a sharp bend and short to the shield.

Last is to secure your bundle with 'string tie'. 'String tie' is nothing more than a waxed nylon lacing cord, usually black or white. Please do not use rib stitch. It is waxed Linen and does not have the same properties as waxed nylon lacing cords. There are several things to know about using 'string tie'. First, if you really tie your knots excessively tight, you could conceivably cut through the Teflon insulation on your wires. Second, just as with ty-wraps, you don't want to tie your knots so tight that they deform the outside wall on a coax.

Having said that, I personally like to use black string tie. It looks sharp and lasts a long time if done properly. I use it in the cabin and behind the panel only, though. When it gets into the 120 to 160 degree range inside your cockpit, the wax on your string will get soft enough to congeal. It has to get extremely hot for the wax to 'melt' off the nylon allowing the nylon to dry up and the knot to unravel. The knots that I use are quite simple and will be demonstrated in virtually any book on knots. First, tie a clove hitch onto the harness, then tie a square knot to secure the clove hitch. Trim the ends of the knot back so that there is about 1/8" to 3/16" of cord coming off of the knot. It might take a few practices to do this well, but it becomes quite easy after just a few tries. After tying the first 8', remove the harness from the first clamp and swing the harness around so that you will tie your harness 'in a straight line'. If you tie your harness up as it is wrapped around the clamps, it will want to keep that shape. (With that in mind, and some good planning, you can actually tie your harness so that it will shape it self for the bends you will need to route your harness comfortably in your airplane. A straight harness will route adequately, its just not as professional looking.)

You will probably want to 'tag' your wires before you tie your harness up. At this time, 1/8" white shrink tubing (5/16" works great for marking coaxes) and a fine tipped permanent marker works great. Merely print onto the shrink tube what the wire is for (i.e. NAV LIGHT or COMM ANT.) and shrink it onto the wire approximately 3" from the ends of the wire.

Your harness(es) is/are now tied and tagged, but not quite ready for your airplane. Wires that are going to the switch panel or breakers can be 'broke out' individually, tied, and terminated (ring terminals installed) so that all you have to do in the airplane is hook up the proper terminal to the right switch or breaker. Say, for instance, your switches are spaced 1" apart on your instrument panel. If you have already determined what switches are for what system, then it is just a matter of breaking out your wires to correspond with your switch placement. The same can be done with your ground wires, instrument dimmer wires, etc.. You should always leave enough wire length to allow at least three terminal replacements (approx 1 1/2 inches).

Congratulations! You have just completed 85% of your wiring job in the comfort of your own home. All you have to do is route the harnesses in your aircraft, secure them to the airframe, and hook up the loose ends. Instead of spending two weeks running one wire at a time, you'll spend, at most, two days routing and connecting wires to the appropriate system fixtures.

A professional job is one that evolves out of good planning and good technique. Just a little effort can make the difference between a rats nest and "GOOD JOB!"

about materials

BUY aircraft quality electrical supplies. Period. You can buy a cheaper gyro, you can shop for a good price on your radio, you may have to purchase a less expensive leather for your interior, but none of these items are as prone to starting a cockpit fire as the quality of your wire, terminals, switches, and circuit breakers. Yes, this is the experimental market. But when it comes to building in, not potential, but probable, electrical failures that might be VERY costly, the money you spend up front may be the best life insurance you ever bought.

The argument that there are alternatives, that these products or those products are OK to use, might be good with both feet on the ground. I personally want to stick with supplies that have been designed and tested for aviation use. Wire, Coax, Circuit breakers or fuses, terminals, and switches, these are items that I want to discuss.

WIRE: There are three types of wire that you want to use, all of them are Mil Spec wire. Of the three types, there are about 10 to 20 variations of each type. The variation is not important, the type is.

FIRST; MIL-W-22759/16-XX. This wire is a single conductor, multi-strand type, that is the most popular aircraft wire on the market today. The only part of that number that really concerns you is the 22759 and the XX. The XX is the gauge wire size (AWG). For instance, if the XX was 20, then the wire size would be 20 gauge. If XX was 2, then it would be 2 gauge wire (battery cable). There are 21 variations of '22759' listed in AC 43.13-1A. All are suitable for aircraft use.

SECOND; MIL-W-81044/--/XX. Here again, the only number that really concerns you is the 81044 and the XX. As before, the XX represents the wire size. This wire is also of the single conductor, multi-strand type. THIRD; MIL-W-27500/ZZ-XX-N. This wire is a multi conductor wire, with shielding. As before, the XX represents the wire size. The 'N' represents the number of conductors in the shield. If we order MIL-W-27500/16-22-3, we have asked for 3 conductors of 22 gauge wire in an ETFE Teflon insulation and shielded wire. From a wire standpoint, these three are the cats' meow. It just doesn't get any better than this.

For all of you who want to use 'automotive wire', just keep in mind that it won't be the flames that'll get you, it's the toxic fumes PVC insulation gives off that will do you in. Teflon stinks like no stink I can describe, but you can still breath. Another thing is PVC will continue to burn with very little heat. Teflon insulation will self extinguish if the heat is not maintained.

COAX: RG-58 A/U. Unless a manufacturer specifies something different, this will do the trick. Just like wire, there are about 15 variations of RG-58 coax. A/U is the best of the RG-58 coax for our purposes. It has a dense shielding, and a quality insulation around a multi-strand centre conductor. What you want to stay away from is solid conductor coax, or RG-58 that has a soft, white foam insulation in it. It is not as durable under heat primarily. And do not route any coax forming sharp bends. The centre conductor will tend to migrate to the inside of the bend and possibly short on the shielding. If you don't use good techniques to install coax, it will give you problems eventually. While I am addressing coax, let me mention coax connectors. Save yourself from long term problems and use crimp on BNC connectors. If you don't have the proper tooling, get your local radio man to crimp them on for you. If he tells you he solders all of his BNC's, do yourself a favor and look further. Over a period of time, solder type BNC connectors have a tendency to pull apart, or at the very least, lose good grounding to the shield. If you can rotate the body of the connector on the coax, the coax connection is bad. It is best to cut it off and replace it with a new one.

CIRCUIT BREAKERS and FUSES: I'm often asked if I have a preference. It all depends on the type of flying that I am doing. Fuses are fine if all you are going to fly is Day/VFR and not in congested areas. Otherwise, fumbling for a replacement fuse as you are being vectored to the final approach, or at night with a flashlight in your mouth, can lead to an awkward, if not fatal, situation. And half the time you grab the first fuse you can find, only to find you've installed a 1 amp fuse instead of the 10 amp fuse that you needed.

I personally like pullable circuit breakers. On one occasion I was flying between Houston and San Antonio, Tx. when I noticed smoke filling the inside of my turn coordinator. In a Cessna 172 (factory equipped) there is a nice, neat row of circuit breakers. Unfortunately, you can't pull them to disable the circuit. "So there I was" at 4500', one eye out the window looking for a place to land, one eye on my turn coordinator hoping not to see those fingers of flame. I've got another eye on my comm radio to make sure I'm on a frequency that will do me some good (being I am in no-mans land), and one more eye on the circuit breaker, praying that it will pop out soon. This, all the while knowing that emergency procedure for an electrical fire says turn off my master switch, turn everything off, turn my master switch back on and then my systems on one at a time to isolate the source of the smoke or fire....excuse me, I knew the source of the smoke, it was just that I couldn't 'turn it off' without turning everything else off. And if I turned everything off, I would lose my radios, comm, transponder, and all! I couldn't pull out the lousy circuit breaker. Ask me sometime how much it would have been worth to me to have been able to reach over and pull out the circuit breaker. Trust me, I would have paid more than the cost difference between resettable circuit breakers and pullable ones!

IF YOU MUST buy used circuit breakers, PLEASE... test them before you install them. Used circuit breakers are usually old . What you won't see is that the contacts are corroded together, and instead of popping at 5 amps like the little button says, it'll take 20 amps before it will pop. If that is the case, the next time it pops will be at about 2 amps (if at all) because the heat sensitive mechanism inside has been fried. Of all the money you spend on your airplane, new circuit breakers don't cost, they save. They save you from frying your electrical systems. Burn up the power supply in virtually any piece of avionics and what it will cost you to have it replaced will easily have paid for your circuit breakers! They may even save your life.

TERMINALS: What is commonly called an 'automotive terminal' is so sub-standard for aviation use, it isn't funny. Even the term 'automotive terminal' is an oxymoron. These type terminals haven't been used in cars for the last 40 years! Here's the problem with them. They have a soft copper alloy base that is tin or nickel plated. That, in itself, is not bad. It is the properties of that metal that make it bad. When those terminals are exposed to a temperature range of as low as 0 degrees or lower in the winter to 180 degrees under the cowling or behind the panel in summer, that metal expands and contracts with the temperature. Over a period of time, the metal becomes brittle, it no longer contracts, and you have a permanently loose electrical connection! If you haven't experienced it, ask anyone who has a lot of electrical experience if they have ever been able to pull a wire , or has seen a wire pulled loose, from an old terminal or butt splice for no apparent reason. Now you know the reason. An aviation grade terminal has the same basic metal terminal, but it also has a second sleeve around the crimp portion of the terminal. This second sleeve has to reach a greater temperature range before expansion and contraction comes into play. The amount of compression you put on your aviation quality terminal today is the compression that will be on it in years to come. This second sleeve of metal also extends past the metal terminal barrel. When this portion of the sleeve is crimped with the proper tool, it forms a rigid diamond firmly around the wire insulation without compressing the wire itself, providing proper strain relief. This prevents the wire from flexing right at the point of compression, know as the fracture point. The plastic insulation on an automotive terminal will not hold nor maintain this strain relief due to the flexibility of the plastic.

SWITCHES: Is it really good to use an AC rated switch for DC purposes? Possibly. I don't recommend running down to your local hardware store to buy switches for your airplane. They do, however. carry some that would suit the bill for some applications. Your safe bet is to get a DC rated switch if possible. Most all switches have ratings printed or molded onto the side of the switch housing. If you do use an AC rated switch, try to use one with at least a 3/4 horsepower rating. If you can find switches with an MS35058-X number on them, that would be your safest bet. These are a toggle type switch.

Your best bet for securing aircraft quality electrical supplies is from your aircraft supplier. I'd venture a guess you didn't go to your local hardware store for your gyro's, fabric, or aluminium sheeting. Why would you go there for your electrical supplies? Virtually every major aircraft supplier carries aviation grade electrical supplies. (Although not everything they will sell you in the way of electrical supplies, in my opinion, is worthy of putting in an airplane.)

tools

Whatever type of project you are dealing with, there is probably some specialized tooling that you had to, or will need to purchase to do your construction. Most people don't have Epoxy pumps just laying around the house or a 3X rivet gun with a good assortment of Cleco fasteners. The majority of homebuilders have had to obtain some special tools for the construction of their airplane. For under $150.00 you can buy NEW tools that will enable you to do an airworthy quality job on all of your aircraft electrical wiring AND coaxes in your airplane, excluding your battery cables. If you know exactly what you are buying, you can find used tools that will do the same job for under $75.00.

If you inspect a piece of MIL-W-22759, you will find that the conductor is made up of very fine wires. Compressing a terminal onto these wires is critical. If I take a bundle of pencils and wrap banding around them just right, I can't find any loose pencils in the bundle. If I wrap them just a little too loose, I can remove pencils from the centre of the bundle (which would equate to a poor electrical connection INSIDE my wire). If I wrap the outside of my bundle of pencils too tightly, I will break the outside layer of pencils. If a 22 AWG wire has 26 strands of fine wire and you find that four or five strands are broken, then the capacity of the wire at the point of compression has been compromised by 20%. You might just as well of started with a 24 gauge wire and crimped it correctly, right!? The best general crimpers that you can get is an AMP product called a PRO-CRIMPER or a similar crimper. Any AMP dealer or aviation electrical tool supply co. should be able to get one of these ratcheting crimpers for you. They should be easily found for under $90.

The major advantage of these crimpers is in the design. These crimpers have a spring that is triggered by compression load. If I insert either a 22, 20 or 18 AWG wire into a red terminal, having different size diameter of wire, I would get a different compression ratio if the jaws of my crimper merely came to the same place each time. This tool does not always close to the same 'place'. It senses the compression being applied to the terminal and the wire, and once the proper compression is reached, all your squeezing of the handle is transferred into the spring. You cannot under or over crimp your terminations unless the tool is out of calibration. Provided you don't use the tool for a hammer, or drop it from the roof, chances are you'll never use the tool enough to justify a go/no go compression check. This tool also provides for two separate crimping patterns in one step. It provides for a rectangular crimp around the wire for a more uniform compression across the wire, and a diamond pattern around the insulation of the wire to provide strain relief. It is very undesirable to have anything flex right next to a point of compression. There is a high probability of fracture. By providing strain relief, even 1/16th of an inch from the compression point, there is less likelihood of wire breakage. These crimpers will crimp red, blue, and yellow terminals, or 22 to 10 AWG wire. Virtually every wire in your plane except your battery cables. For the record, when using aviation grade terminals, red terminals are for 22, 20, and 18 AWG wire, blue terminals are for 16 and 14 AWG wire, and yellow terminals are for 12 and 10 AWG wire.

Another advantage to these crimpers is that they have removable "jaws". For a reasonable price, a second "jaw", or die, can be purchased to crimp on BNC connectors. The BNC connectors that I use are AMP P/N 225395-1 (Male) and 225396-1 (Female). It is unfortunate that one tool can't crimp all manufacturers' terminals and BNCs. (Its just as unfortunate that Chevrolet parts won't fit on a Chrysler, if you ask me!)

Just like crimpers, there are a lot of wire strippers out on the market that are great for use on household wiring. Not too many are good for aviation use. Just remember one word; STRIPMASTER. No better stripper available for the price. One can find these strippers at most commercial electrical supply outlets. New price will range from $15 to $40. There are a lot of "copies" out there, so look for the Stripmaster name on the spring cover at the centre pivot point. The advantage of this type wire stripper is that while one set of moveable jaws holds the wire by the insulation, another set of moveable jaws with 360 degree cutting edges for each size wire, cuts through the insulation on the wire without nicking the wire strands. The last and continuous action while pulling the two handles together on this type stripper is it will gently pull the insulation off of the end of the wire. There is no rotation needed of the cutting edges like most cheap wire strippers require. This rotating action usually results in the nicking or cutting of wire strands under the insulation. Other types of automatic strippers (not suited for aviation use) typically cut through the insulation with two parallel blades and then literally rips the insulation off. These tools usually takes a few strands of wire with it, too.

For those of you who wish to do your own soldering when it is required, a 40 watt pencil iron from Radio Shack should do quite nicely. Be sure to get a 'flat' tip for it (approx 1/8" wide). Pin tips generally don't apply enough heat, quickly enough, to the area needed for the type joints one will usually encounter in aircraft systems.

To complete a well rounded assortment of electrical tools, you will need a flush cut pair of wire cutters. There are several types of cutters, diagonal, semi-flush, and flush are the most popular. The main reason for wanting flush cut cutters is that when you go to trim your ty-wraps, if you are not using a ty-wrap tool, diagonal and semi-flush cutters will leave sharp edges on the 'tail' of your trimmed ty-wrap. These sharp edges will be present even if you try to cut as flush to the locking mechanism as possible. This won't prove to be a problem until you have to reach up behind the panel. Ever pick blueberries without a long sleeve shirt? I hate sharp edges on ty-wraps!

Anyone who makes a living with their hands will tell you that the right tool for the job makes all the difference in the word. Wiring an airplane is frustrating enough for most people. Having the right tools will make the job a lot easier.

soldering

A few tips on soldering. First, contrary to popular practice, no matter how hard you press on the solder joint with your iron, it won't get any hotter. It'll just bend the soldering iron tip or deform the connector pin or both. Heat is transferred through solder. Be sure to have a moistened sponge around when you solder so that you can continuously clean your tip as you work. Merely stroke the tip lightly across the sponge (both sides of the tip) and 'wet' the tip with solder. Wetting the tip means applying just enough solder to the tip to lightly coat it. If you have a big ball of solder on your tip, all that will be accomplish is a big mess around your solder joint.

Second, 'tin' the wire end and the socket. This is done by applying just enough solder to the wire to penetrate the strands of wire. If too much solder is applied it will 'wick' up underneath the insulation. That is not desirable, especially if it wicks too far up under the insulation. A lot of intermittent problems occur with soldered joint when solder has wicked up under the insulation. If forms a rigid fracture point under the insulation and after repeated bending or vibration, the wire will break at the end of the solder. Troubleshooting these kinds of intermittencies are a real pain since the visible joint appears to be fine. To properly tin the end of a wire, lightly wet the soldering iron tip and hold it on the end of the wire. Place the end of the solder about 2/3 up the exposed wiring and wait for the solder to flow. Since solder flows toward the heat, the solder will not tend to 'wick' up under the insulation. This wicking action usually occurs when the heat is placed where the solder should go and the solder is introduced to the wire on the end where the soldering iron should go!

Next, a socket should be filled approx. half full with solder. Once both the wire and the socket are tinned, it is just a matter of holding the wire near the mouth of the socket, apply heat to the socket, and when the solder in the socket becomes fluid, insert the wire and allow the two to 'flow' together.

If tinning your wire or socket, or soldering your wire into the socket, takes more than just a few seconds, check your technique and / or your equipment. First, is your soldering iron clean and properly wetted? Second, is the wire or the socket corroded or oxidized? The metal surfaces should be clean. Flux can be used, but sparingly. And be sure to clean any excess flux from your joint after you are finished soldering. Flux, when left exposed to air for a period of time, becomes corrosive. Isopropyl Alcohol can be used to clean the excess flux away from the soldered joint. Last, make sure you are not trying to heat too big a surface with your iron. All things being right, if it takes more than 4 or 5 seconds to properly heat the surface that you want to solder, you really need a hotter iron. Your soldering iron will do most of your wiring.

simple soldering rules

Don't...apply heat too long to a surface
Don't...apply too much solder to a surface
Don't...try to solder dirty, corroded, or oxidized surfaces. Clean them first.
Don't...solder wire ends and then crimp terminals on
Don't...crimp on terminals and then solder the wire end
Don't...solder any connection that is not 'solder specific'. Most connectors use either a crimp pin or a solder type pin.
Do...make sure that your tip is properly maintained
Do...make sure surfaces are clean and bright
Do...Solder with discretion. Solder joints are the one biggest problem that I have to deal with when I troubleshoot someone else's work.
Do...Practice soldering before you tackle your radio harnesses. It's a lot easier to do a job right the first time than to have to do it a second time.