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Wiring harness compatibility

Dan Starc

NAXJA Forum User
Hi Folks

I have a question about wiring...are the wiring harnesses in a 1987 and a 1989 XJ interchangeable? I ask this as I may get a chance to move most of the parts from an '89 into an '87. The harness in the 87 looks a bit different; there's a funky connector above the brake booster, which is not present in the 89. I have a friend with two 1988 MJs and one has this connector, the other doesn't.
I would like to leave the harness of the 87 and plug it to my 89 motor and tranny...would this work ok?

All Jeeps in question here have 4.0 non-HOs with AW4s.

Any help would be appreciated.
 
They are essentially the same ... but

The connector above the brake booster is the C101 connector. That was troublesome, and there was a factory TSB (technical service bulletin) describing how to remove it. This was a mid-year change in the 1989 model run. Essentially, the 89 harness has the same wires but they are solid at that point rather than run through a connector.

Also, the 87 did not have a ballast resistor for the fuel pump.
 
There was a TSB for adding the fuel pump ballast resistor, too, so yes ... it can be added. Donno where/how you'd want to do it. It can go anywhere between the fuel pump relay and the pump, but there's also a circuit to bypass the resistor when starting and I don't know if that circuit is already there on the 87s or if it has to be added.

Best approach would be to get an 88 or 89 wiring diagram and just follow that.

The ballast resistor just reduces the voltage to the fuel pump so it runs slower. The purpose was to reduce noise. Funny thing is, my 88 XJ has it and my 87 MJ doesn't, but the MJs fuel pump is quieter than the XJs. I wouldn't worry about it. Ballast resistors do fail, so omitting it gives you one less thing to go wrong.
 
Thanks again Eagle
So, my 89 fuel pump will run just fine without the resistor? TSB #?
And to continue abusing your knowledge, where do I get access to the TSBs that I may need to do this swap? I mean, the removal of the C101 connector, is this an actual TSB?
Would it be easier to get another '89 instead of the '87? Does it really matter?
I really appreciate any help, as the project seems quite daunting unless I get more informed about it.
Thanks!
 
Don't know the TSB number. Maybe someone with a Carfax account can call it up for you. Basically, it called for cutting the wires where they go into the connector and soldering each pair ... emulating what you see on your 89. I had a dealer do mine before I knew any better. The service manager told me it would improve fuel economy, improve emissions, and cure a condition called "early morning drive-off stall." Of course, it didn't help any of those things, and when I spoke to the service manager about it later he denied ever saying that.

So the '88 XJ has had the C101 bypass performed and the '88 MJ has not ... and they run equally well.
 
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