Making or Repairing Wiring Harnesses
by Dan Masters, firstname.lastname@example.org
Whether it is advisable to make your own harness, as opposed to repairing the existing harness, depends on a number of factors. If you have no harness at all, it would be much easier and cheaper to buy a ready made harness. Building a harness from scratch, without a pattern to go by, is extremely tedious, to say the least. If, on the other hand, you have a fairly good harness, with only a few wires damaged, then it would be cheaper, and almost as easy, to do a repair. These two extremes make the choice fairly easy; it’s when your situation is somewhere between that the decision is difficult.
A common situation is to have one or more harnesses that have been salvaged from the junkyard. In this case, it may be desirable to save as much of the harnesses as you can, re-using the connectors and wire to make a new one, or to repair the better of the harnesses to make one good one out of those that you have.
As for re-using the connectors, I would advise caution. Of all the pieces of the harness that give problems, the most likely is the connectors. If you do re-use them, make sure they are clean and corrosion free. The bullet connector sleeves, the black pieces that are used to connect two pieces of wire, are particularly trouble prone. Often, the metal sleeve inside will crumble with age, and will no longer have sufficient tension to make a good connection (not being a metallurgist, I can’t explain this, but on about six of them on my ’71, when I removed the bullets, pieces of the metal sleeve fell out on the ground).
Salvaging the wire is not a problem, as long as the wire has not been damaged. If you can, i.e. the wire is long enough, I recommend cutting the wire an inch or two from any connector. Often, moisture will wick up the strands and corrode the wire, making it difficult to get a good connection. You should cut back to where the wire is clean and shiny.
The easiest way to repair a harness is to clear out a large space on the garage floor, and lay the harness down, stretched out, with each “leg” of the harness laid out by itself. Strip back the tape surrounding the damaged area, being carefully not to displace the wires from their original position. Lay the new wires down, one at a time, alongside the original wires, to make sure they are the same length (allowing 3/4 ” overlap for the splice). Strip off 3/4″ of the insulation from both the old, and the new, and slip a piece of heat shrink tubing over one of the wires. Twist the wires together, and solder. After the joint has cooled, slip the heat shrink tubing over the joint, and apply heat to shrink. Attach whatever connector is appropriate to the free end of the wire. Continue with each wire, till that section is done, and then go on to the next section. Use plenty of cable ties to hold the wiring in place as you work, prior to re-wrapping. As you come to each cable tie, during the re-wrapping process, cut it off, and discard it. Be prepared to use plenty of cable ties.
Don’t make all the splices in exactly the same place. If you do, the wire bundle will be very thick at this point, and all the stress will be concentrated in this area. Space the splices out over the length of the harness, at least six inches between each splice, if you can. Don’t worry about making splices, the factory did it themselves.
When you do the re-wrapping, begin with the terminal, or connector end, and work back towards the main harness. That way, you have fewer loose ends of the wrapping tape to worry about, as the wrapping for each leg gets wrapped again by the main wrap. Start by running a short piece of the harness tape parallel to the wires, heading towards the connector end, and start wrapping back over this piece, back towards the main harness. This way, the wrapping