72 CSi wiring diagram

[ScottAndrews]

If it was my car, I'd take each wire, identify it by color and location using the diagram, number it with a wire label according to the diagram, and locate the other end and label that. Once you have done that. connect both ends where they are supposed to go and move to the next wire. Tedious, but it should both get the wires back to where they belong, and show up any weird modifications. If you get stuck on a modified wire, move on. Eventually 99% of it will be connected correctly, and you can then resolve the odd parts.

 

[rsporsche]

My earlier comment… Just saying.. if unplugging the taillight solves and/or creates the problem I thought it would might be simple to trace back from there …but… I see you have many extra slices and splices.

the taillight wiring runs from the light switch, brake light switch or turn signal - from under the dash, down along the side of the drivers floor and back to the light fixtures. they aren't interrupted or start / stop / restart. you should be able to look at the female spade connectors on the light fixture and see if there is any damage. if there is damage, there will likely be damage on both ends ... this means you need to redo both ends of the wire. i think the culprit here is the lack of ground, once fixing that, to complete the circuit, that should be good. but as we know, there are 4 parts of the taillights - reverse light, running lights, brake lights + turning signal. the ground is common to all of them, but each has its own signal / power wire.

 

[restart]

I am confusing if nothing else!

After my simple fix comment..

I looked at this attached
(Chris original poster pic)
And ASSUMED it was a pic of some kind of post factory wiring cut/splice. I can’t tell.

A few wires hidden under tape can hold a world Woff mystery.
Enjoy the pursuit! Good luck.

Wiser minds prevail
That’s my final answer.

 

[ScottAndrews]

Yep, that's a ground connection...