Tell me how to rewire a vehicle

Question:

My 1951 Studebaker Champion is all original and very presentable, with a good interior and very nice paint, but the wiring under the dash and in the engine area is stiff and crumbly, and some of it has been bypassed with modern wire that doesn’t look right. How hard is it to rewire a car?

Answer:

The job is not as difficult as it looks. i It can be done at home with hand tools, and the sources listed below can provide a complete, properly-color-coded, authentic-looking wire harness for a modest sum. It will come with all the correct ends, and each wire will be numbered. All you have to do is follow the list provided with the harness. Be sure to give the harness manufacturer the make, year and model of your car, and such information as whether it has overdrive (you'll need an additional sub-harness for that) and whether it has a radio, heater, automatic transmission or other accessories.

Some harnesses will not have wires for all the possible accessories and in that case you will need a couple of spools of wire in the correct colors and gauges, as well as some connectors. You will also need electrical pliers with the gauges marked on them and builtin strippers as well. A continuity tester is also nice to have, but an automotive light bulb and socket with one wire attached to the button on the end of the socket and the other attached to the side will also do the trick. Add alligator clips for convenience. To verify if a wire has current going through it, merely touch the wire from the end of the socket to the wire, and touch the other wire to a grounded part of the chassis. If the bulb lights, you've got power.

You may also want a small soldering iron and a roll of solder. On six-volt cars such as yours, I like to solder the connections and splices, because there is so little current going through them that if they are the least bit corroded or the connections are marginal, you will have a problem. The only downside to soldering the connections is that if you get the wires too hot, they may become stiff and prone to breakage.

One of those assortments of wire clips, splices and connectors they sell at electronics stores will come in handy for the odd situation where you need to make a wire that is not included in the harness, such as might be used for after-market fog lights. And don’t forget the black electrical tape. Heat shrinking tubing in the right diameters is also useful for insulating connections.

Order your harness, and while you are waiting for it to arrive, find a wiring diagram for your car and familiarize yourself with it. It takes a little head scratching to figure out what the symbols mean, but once you know what connects to what, you can proceed with confidence. You will see that there is a lot going on, but if you trace one wire at a time it is simple to understand. You can also take the old harness out of your car while you are waiting. But before you do anything, remove the battery and set it aside. Don’t neglect this step because if you don’t remove the battery you could cause a fire or burn yourself, and/or ruin components. Only reinstall it after everything is hooked up and you are ready to do some testing.

These are the things you need to replace a wire harness.

Don’t be intimidated by all those wires. Just start under the dash and disconnect everything systematically. If possible, pull the old harness in through the firewall uncut so you can compare tt to your new harness for length. It is OK to cut the old harness, but do it as sparingly as possible.

Once the dash is cleared, disconnect the wires to the charging system, headlights, directional signals and other items. And then disconnect the taillights, license plate light and other wiring in the rear including the gas gauge sending unit on the fuel tank. This is probably the most challenging thing you'll have to do, because it usually means dropping the tank enough to get to the sending unit.

When your new harness arrives, lay the old one out in your driveway and lay the new harness over it. Is it the correct length? Ts everything there? In most cases, they give you plenty of wire. Familiarize yourself with the harness and where things go and then—starting from under the dash— put the harness loosely in place. Don't start attaching things until you have the harness located throughout the car because you could get it bound up otherwise and have to undo things to get it to fit.

Use fine sandpaper to clean any corroded connections on the original components until they are bright metal and then attach the wires. I like to put a little dielectric white grease on each terminal to keep it from corroding. I live three blocks from the beach, so corrosion is a problem. However, I rewired my 1940 Packard 30 years ago using solder and white grease, and have had no problems since. You may want to use heat shrink tubing or electrical tape to insulate the connections.

When the wiring is all hooked up, put the battery in its box and attach the ground lead. Now, with the hood lowered a bit and in a darkened garage, just touch the hot wire to its battery terminal. You may see a tiny spark initially if your car has an electric clock, but if you get a big spark, leave the battery disconnected and go around making sure the lights and accessories are all turned off. If you still get a bot spark, you will have to trace down where you may have a short or open circuit.

Finally, be sure to polarize the generator according to the instructions in your shop manual before starting the car. That's it!

Now your car not only will look correct, but the new harness will be trouble-free and last even longer than the original.

Here are a couple of sources that I have used:

Y and Z is an outstanding source for original harnesses for older cars. Their quality is excellent and the directions are easy to follow. https://www.ynzyesterdaysparts.com/

Painless can supply totally original harnesses as well as custom after-market examples so you can add air conditioning, modern accessories, an alternator, extra fuses and an auxiliary fuse block. You can reach them at:: Painless Performance Products https://www.painlessperformance.com/