Wiring harness help

[Axeman]

ok here's my problem, the dash wiring harness on my '75 is pretty hacked and could be a source of electrical fire in the future if I don't take care of it. Luckily I just picked up a nice factory untouched complete dash harness out of an 87/88 Carrera for dirt cheap. I figured it would much easier for me to replace the whole harness, vs trying to spend weeks trying to figure out where it's hacked and fixing it.
How much work is it for me to swap out my old one with the new one? Since I'm in the process of adding power windows and other things, such as newer 993 fog, defroster, etc switches, I think this would help me out. this would be my first time pulling out a harness out of a 911 and I can use all the help I can. What's the easiest way? Removing the front heater stuff, then start unplugging and marking where every color wire goes to?
Thanks for any advice.

[targa80]

Before you start this project may I suggest that you acquire schematics for both vehicle harnesses. Then do a comparison on the exact differences. I doubt very seriously that the 87/88 will just drop right in. I have pulled my harness on my car and it breaks down into 3 or 4 major wire harnesses that interconnect at different components. I work with electronic/electrical circuits every day and have the skill to reinstall the harness with hopefully minimal problems. I will be using a schematic and wire labels I put on the harness as I removed it. I also took some digital photos of areas where there were a lot of connections to components. My suggestion to you would be to go through your original harness and repair it or purchase a like kind harness.

Other than that good luck with the project.

[Axeman]

Thanks Pat,

I will probably take mine out and make sure I label where everything is connected to, and take pics as well.
I will compare it to the new 87/88 I have and maybe just use the portions that I need and add things that I want to have, like power window harness, etc.
Where can I get some really good diagrams for a 75 and a 87/88 Carrera?
There's an 82SC on this site.

Thanks!

[filou]

like it was advised to you, You'll need to acquire schematic for both wirings harness and go from there. Can you read and understand wiring diagrams ??? not to hard, once you understand the concepts.
For each connections, note color, size and numbers of wires for a start !!!
Look at your new harness and test it for contnuity and realize where each of those wires start and finish. I believe the wiring harness breaks downs in "sub-divisions" out of the whole harness. Start from one end of harness, match the wires you'll be using and test for contunuity(new harness) before you disconnect old harness. Once you are sure that the wires are correct Then change harness. Put same info on old harness wires and new ones in case something doesn't' work, you can always backtrack it !!!!! By spending a little extra time as you go, marking your wires, you might save time and headaches in case of trouble.
good luck and a lot a patience !!! Don't rush and be very methodic and understand what you are doing.
Start from one side of both of your schematics (old and new harness), a circuit at a time. Cross with a pencil when you are removing a wire from the old harness and highlight what you are doing on the new harness schematic.
Truly, Phil.

[304065]

What, exactly, is wrong with the old harness?

They aren't a direct swap, unless you plan to rip the whole car apart, pulling the old harness and putting the new one in is a MAJOR undertaking. If it were me, I would identify those wires that are in rough shape, cut them out and solder pieces of the 87 harness to replace them, to the extent the wire colors are the same. This would save you some fabrication time, certainly.

I can only imagine what a nightmare it would be to remove everything, try to log where every connection went, and then fish the late harness back in place, connect everything up again, including new stuff, modify the new harness to adapt to the old stuff, and expect it all to work right. You probably could get it done, but I would plan on a few dozen hours to do it right. Not trying to discourage you but I've spent hundreds of hours working on my wiring harness and I can tell you, when I restore an early car, I'm going to photograph everything and then order a new harness from www.ynzyesterdaysparts.com and put that one in.