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Help please: Renix wiring harness interchange

tchase

NAXJA Forum User
Hoping someone knows this off the top of there head as my weekend project for the MJ is currently stalled at 4:30 friday afternoon. Not a good start.

Anyway the question is; will an '89-90 engine compartment harness plug into an '88 interior harness? I wanted to swap out my badly hacked and rotten harness but I didn't realize the the donor harness was different. Got comparing the two and noticed the big plug located by the the emissions tag on '87-'88's was missing from the donor. Is this the only difference? Are the pinouts of the firewall connector still the same?

I'd really appreciate any input here as I don't want to continue tearing my harness out if I can't make the donor work.
 
As far as I know 87 was a bastard year since it was the first. and I beleive 88-90 should be same/really similar.
 
Not sure on exact changes, but the C101 POS bulkhead connector was eliminated 89+, so you are going to have to do some modding for it to work.
 
i'm not 100% on this, but looking at my mj('90), and from what i recall about my '87 xj, the harness should attach at the fusebox outward with no issue. afaik, the only difference was the elimination of the c101 connector, which you DO NOT want anyway. that thing is a the scourge of the early renix.
 
IIRC, 87 and 88 had the C101 and in 89 it was eliminated. I'll know for sure by next week when I get my 89 Cherokee Limited parts Jeep. I have an 88 XJ with the C101 and a 90 MJ without it.
 
My 89 parts Jeep had the new style harness, without C-101. It's been a while since I had it, and I sent most of the wires to 5-90 long ago, but my recollection was that the engine control wiring went straight through the firewall to the ECU. There was no bulkhead connector.
 
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Update:

First off, thanks for the replies. Even though nobody knew for sure if it would work I was encouraged by the fact that nobody knew it wouldn't work, lol. I did some checking on wiring diagrams and ecu pinouts etc. and couldn't see anything definitive that it wouldn't work so I went ahead with the swap.

Now for a little background on my particular situation. My MJ was an original 5spd, but about 4 years ago we swapped in an AW4 to replace the A999 t-flite the previous owner had swapped in. The swap was extremely rushed as we were trying to get ready for Jeep Jam. Patched the AW4 wiring into the MT wiring harness in about 3 hours and it's worked great for the past 4 years. Now over the past few years the green monster has started spreading through the original harness. Problems with the front lights, horn, ignition power, etc etc etc. I've been splicing wires and bypassing plugs for awhile now and it was starting to get really aggravating. Recently I started having major shifting problems and then random no starts. With the octopus of splices and bypasses it was getting impossible to know where to start looking for problems. With Jam coming up in just over a month I really needed to get the truck reliable again.

So I tore out every wire from firewall to headlights and started over. Donor harness was from a '90 automatic. Plugged everything in and undid a few bypasses in the interior harness. Much to my delight it fired right up and pretty much everything worked right away. The only issues involve mating the AW4 engine bay harness to the 5spd interior harness. Things like the brake switch input to the trans controller, the power/comfort switch, back-up lights etc. There are differences in how these are routed through the harness between the early and later models. The '89-'90 engine harness has a 6-pin connector under the dash by the ecu plug for these things. The earlier harness only has a 3-pin connector here which is for the brake input, trans input power, and power/ comfort switch. So I haven't figured out the back-up lights yet, but overall it's a successful swap.
 
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