Help: TJ transmission swap and fun with wiring harnesses... Yay! - JeepForum.com
 
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post #1 of 7 Old 09-28-2015, 09:30 AM Thread Starter
JMH77
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2004 TJ Wrangler 
 
Join Date: Apr 2015
Posts: 40
Help: TJ transmission swap and fun with wiring harnesses... Yay!

It's a discussion that has haunted the forum forever... but here we are again. Only this time... it's a swap between year models and transmissions. I hope somebody can help shed some light for me...

Here is my project: I have a 2004 TJ (originally with a 42rle trans)... and a 2000 TJ (wrecked donor vehicle originally with a NV3550 trans). I'm rebuilding the '04 from the ground up and swapping over the NV3550 from the 2000. All of my mechanics, clutch, flywheel, etc, etc are complete. The manual trans is installed and I have it mated to a 241 t-case I sourced elsewhere. I'm in the final stages of buckling everything up.

I need to clarify a couple of electrical concerns though... The Jeep is keeping it's original engine/transmission harness from the 2004 4.0 that had the 42RLE but I've got it plugged into the PCM originally from the 2000 donor manual. Basically, I just removed the '04 PCM and TCM and auto trans... but kept the harness. I then installed the NV3550 from the 2000 with it's corresponding PCM. So, I'm left with several connectors from the auto harness I won't be using... no biggie. Here are my questions:

- Which plug on the vehicle side harness is for the Crankshaft Position Sensor? I now have a CPS on the driver side of the NV3550 which I need to somehow wire into the harness (originally '04 42RLE). I think there are 3 black wires on the Mopar CPS. I'm assuming they need to be changed around and adapted to the auto harness. Which plug is it on the auto harness? I think it's right by the starter and oil pressure switch somewhere. And more specifically... which pins need to be swapped around?

- I also need to address the backup light switch. Again, I'll need to figure out how to adapt the backup switch on the NV3550 to the old 42RLE harness. From what I've read, I think pins 1 and 6 on the range selector plug handle the backup switch. Not sure though... can anyone confirm?

- Finally, the only thing left would be to adapt the 241 tcase 4wd position switch and speed sensor to that harness as well. Hopefully that's somewhat easy... but any guidance would be awesome.

I've read some conflicting info... some people say that I'll need the original motor/trans harness for the manual and some say I don't. I do actually have the harness from the manual... but it's a 2000 (not 2004). So, plugs are different, evap system is very different, etc. After some research, I found that it may just be easier to stick with the auto harness and yank the TCM (which is what I did). This way, everything stays the same with the motor, evap, etc. Also, there is no TCM looking for a PCM and the PCM isn't looking for a TCM. By the way, both this Jeep and the donor Jeep are non-skim keys so there shouldn't be any issues there. All I need to do is adapt the CPS and backup light, and make the t-case connections. And... I guess I'll need to deal with tricking the neutral safety switch somehow.

Thank you in advance to anyone who can lend some advice. I've come this far with the project and I'm not quitting now :-) I've read through a bunch of threads regarding trans swaps... and unfortunately the discussion always leads away from technical input and crashes right into personal opinions over who thinks what trans is better, etc. Hopefully we can avoid that and offer up some good technical advice. And even though I'm asking for assistance in this thread, I'm absolutely willing to offer help and share my findings with this swap if anyone inquires. If I've left out any important information that can help with an answer, please let me know. I very much appreciate everyone's input and guidance, thanks again!

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post #2 of 7 Old 09-28-2015, 09:34 AM
87comanche
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1987 MJ Comanche 
 
Join Date: Mar 2006
Location: Somerville, NJ
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On my 2001 TJ, when I installed the ax-15, there was a four wire to two wire connector that plugged into the backup light switch from the new trans. This activated the backup light, but also jumped together the other two wires in the loop, "bypassing" the NSS. I had to get a reman PCM from a 5 speed TJ, programmed to my VIN and mileage. No problems since.
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post #3 of 7 Old 09-28-2015, 10:24 AM Thread Starter
JMH77
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Thanks Comanche. So, you originally had an auto and kept your auto harness? I'm good with the PCM... I have one that's correctly programmed for my NV3550. Sorry, I'm not quite understanding what you said about the wiring though... can you better explain? You had a plug on the harness side that had 4 pins (2 controlled the backup light switch, and the other two you jumped together to bypass the NSS)? Do you recall which plug it was? It's probably different on my year and trans but maybe that will point me in the right direction, thanks again!
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post #4 of 7 Old 09-28-2015, 10:28 AM
87comanche
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It's the same harness your auto had, just remove the pigtail that goes to the trans, and you should be left with this four pin connector. It may be different on your later model, but that's what it came down to for me, and you could just use the short connector from your donor nv3550 backup light switch.

Tom

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post #5 of 7 Old 09-28-2015, 11:51 AM Thread Starter
JMH77
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Join Date: Apr 2015
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Cool, thanks again. I'll take another look at it tonight. The harness has several plugs on it... 2 larger ones, one of which is the green plug (I think range selector or solenoid switch), and then a couple other smaller ones. Do you recall which plugs are what? I've tried looking for a diagram that specifies what each plug pertains to, but no luck finding one. I'm guessing the only one I'm concerned with is the one with 4 wires as you stated. I'll put my eyes on it this evening and see if it makes sense. Thanks.
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post #6 of 7 Old 09-28-2015, 12:00 PM
87comanche
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I don't recall. What I did was unplug everything I could and set it aside with the old tranny. What o was left with was that four pin plug. You will have one more connector, since you have electronically modulated overdrive and mine was a 3 speed auto.

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post #7 of 7 Old 09-28-2015, 12:17 PM Thread Starter
JMH77
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Join Date: Apr 2015
Posts: 40
Ok, understood. I'll see if I can narrow it down and figure out which plug I need to deal with. Thanks again for your help.
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42rle , harness , nv3550 , tj , transmission

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