I've searched but couldn't find a definite answer. I have an 89 MJ 4.0 2wd AW4 and I found a 98 4wd aw4 from an XJ. I've read about building the circuit or swapping the rear housing and speed sensor setup. My question is can I swap the tcu and wiring harness instead?
Again sorry if this has been answered, I scrolled through this post and have searched all over for the answer.
Thanks.
Grabbing the entire 98 trans, xfer case, TCU, 98 NSS, and the 98 wiring harness between the TCU and Trans should work with some minimal splicing required. Other than the wiring between the TCU and tranny/NSS, I think you've only got seven wires that need spliced into the vehicle? +12v ign off, +12v ign on, brake switch, ground, backup lights, tps sensor (see note below about the TPS), and maybe a wire from the NSS to the start relay (interlock so you can only start with it in park).
One thing to note is that the 89 has a dual output Throttle Position Sensor (TPS) providing a "normal" output for the engine, and a "reversed" input for the TCU. The 98 only had a single "normal" output that's fed to both the engine computer and the TCU. So during the swap you need to splice into the other output from the TPS.
The 89 engine computer doesn't talk to the TCU, so don't bother hooking up the data wires on the 98 TCU (in fact, the data wire on the 89 just rruns to the yellow diagnostic connector under the hood). The 89 had the power/comfort switch on the dash that's no longer used, so you can skip that wire as well.
I probably have copies of the relevant portions of the wiring schematics if you need help sorting out the wire colors.
I don't recall if the throttle cable between the 98 trans and the 89 trans is different at the throttle body end. The speedo cable will need to go into the xfer case instead of the back of the 2wd tranny.
