Easiest way to figure this out is to take out the engine bay harness/forward light harness and pull all the wires out of the plastic tubing. Make sure to zip tie the wires together that go off in different directions. I'm assuming you know the wiring in your car and should be able to identify each wire and which is useless/not being used.
This may sound like a chore, but it only takes an hour or two and is well worth it. It was actually very easy IMO and ended up eliminating over half of the old harness. I replaced all the connections and ends, cleaned the wires with paint thinner to take the crud off, and wrapped the whole harness in electrical tape. Once you do this, you know that you will not have any electrical issues in the engine bay. If you want pics of my harness, I can take some and post'em up here.
TO ALL READING THIS, one very faulty spot in the wiring I found is in the plastic tubing down near the starter. There is a metal crimp that connects three wires: BAT alternator wire, air, and one to the ignition. I got rid of the air since I no longer have it and the BAT wire since I'm going to be running the CS144 alternator and will be running a 4 gauge wire directly to the battery. From this crimp one wire goes to the starter to provide power to all three. This metal crimp, at least in my system, was heavily corroded with rust and oxidized wires. This was probably what caused me so much headache with inaccurate voltage readings and sometimes starting.
Sorry this seems to be a bit much, just got done doing this and well worth restoring the harness.
