I am redoing the engine wiring harness in my 6L v12 and have a few questions I hope someone more experienced than I can help with.

It appears that there have been multiple efforts to fix the wiring so I may be dealing with some non OEM stuff. I suspect I will have many questions.

There appear to be at least 4 types of wire being used.

Many older (probably OEM) wires 18 ga
2-4 older wires in 20 ga
2-3 newer runs that appear to be 14 ga
2 wires (1 from each Ignition Power Module to ECU) that are copper shielded parallel wires (2)

Before making the discovery that there are multiple wire gauges I was planning on replacing everything with 18 ga cross link GLX wire. I have 2 areas of concern

1) Shielded Parallel Wires - What to replace the copper shielded parallel wire with? In the attached pictures you should see that at the Ignition Power Module end only the 2 shielded wires progress into the connector and there is a 3rd 18 ga wire that is soldered to the sheathing.

Can someone describe to me why there is a need for sheathing of those 2 wires, why is there a wire soldered to the sheathing, and advise me on how best to replace those runs.

2) In the reading I have been doing on this thread and elsewhere I don't see the need to use anything other than 18 ga wire. Is it OK to replace the 14 ga with 18 ga? (The black wire in the picture is an example of a 14 ga wire)

All help/advice appreciated.

 

When I built a new harness for my 89 Marelli car, I picked up some stranded coax at a local electrical supply house. I really know nothing about electronics, but as I understand it, the wires are shielded because of the signal traveling on those wont be disrupted by wires running parallel to them. It really was no problem soldering onto the shield at all. Mine works great. I took my time, didn't build it exactly as the original, as it had far too much wire, was bulky. I ran mine more "custom"? and it certainly is much more "neat" than the original.

 

I do not recognize the connector in the photo, but if you are CERTAIN that the OEM wiring was only 20 gauge, there is no problem in using 18 gauge. If you are not certain, and do not have a wiring diagram that specifies wire size, then I would not replace it with anything smaller.