86 MJ Swap Electrical Issues

[dastrius]

Hey all! I’ve got some electrical issues going on and trying to see what insight there is on my issue. 
 

I’ve got an 86 MJ that I’ve successfully swapped a rebuilt Renix 4.0 w/ HO Head, and a rebuilt ba10 into (I know, ew). It all runs cherry and have no issues with it up until this point. Now when I did the swap, I used the 88 Engine Harness but kept the 86 Dash harness still in the cab. I’m sure this is where my problem lies but I’m curious to see what others say. When I turn the key to the on position, my turn signal indicators and high beam indicator turn on and stay solidly lit. The illumination lights for the gauges also are slightly on even with the headlight switch pushed in. Along with that, none of my gauges work except for the tach. Funnily enough, all of my exterior markers work perfectly fine. I’ve gone through and checked my major grounds and look to all be properly connected. Side of the block ground, battery ground, dash ground, ground strap on the block, and ground under the air box are all hooked up correctly. Tried cleaning my C101 and had no effect. I also cleaned my C100 Bulkhead while I had it apart. Seems like back feed coming through to my gauges. I’d assume this may be an issue with Jeep moving around the pins on the bulkhead and pins not lining up, but I’m curious to see if anyone has had any issues like this. 
 

Thanks in advance!

-Jared

[eaglescout526]

Well an engine management swap shouldn’t have done that unless power is getting to the cluster when it shouldn’t be. Unless you swapped out the entire engine bay harness, but if it’s an 88, the C100 shouldn’t plug into the 86 C100 due to the terminals being different. 
 

Anymore details on your 86? What engine was originally in it? 

 

when I did my engine management swap in my 84, I just simply cut out the old carb computer stuff and left the original wiring harness intact 

[dastrius]

Hmm odd, I did swap the entire engine harness with the 88’ one but the dash harness is stock to the truck, and it’s October of 85’. It originally had an AMC 2.5 TBI in it before it decided to call it quits. I’d assume a bad ground since I’ve heard of similar issues being caused by a bad ground. I unplugged the headlight harness to attempt to isolate the issue and make sure it wasn’t a bad ground from the turn signal sockets since other forums have pointed that out to be the culprit for similar issues, but still continued to stay lit after unplugging the headlight harness. 

[eaglescout526]

Bad ground would cause the cluster turn signals to illuminate but not the high beam which is odd. Do the cluster lights come on as well? This would lead me to think something is backfeeding the cluster to light those up. Unplug the cluster fuse and the instrument panel lamp fuse and see what happens there. 
 

What’s great is yours is an 86 so it has the good sockets still. Or at least it should. 84-86 and 91-96 AMC/Chrysler used the metal sockets that are better. AMC switched to ford sockets due to them being cheap in 87 and used them until 90 which you should be fine and shouldn’t have to worry about that. 
 

Im super curious on your C100. I know in 88 it uses metri-pack style terminals. 84-86 and possibly 87 used packard series 56 terminals. 

[ThatJeepGuy]

This isnt very detailed but I had an issue with my dash lights and sometimes radio staying on after keyed off. Dealt with this intermittently for years until while updating my headlights and doing the popular headlight harness relay kit I also installed a new headlight switch. Problem was gone after that, when the key is turned to off, everything is off. 

 

Perhaps there's some troubleshooting method to look into on the function of your headlight switch?

[dastrius]

Well thank you for the help guys, I appreciate it. Went in there today and did some inspectin'. Turns out that when I was tugging on cables to wiggle the new ECU into it's place, I must've accidentally tugged on the harness going to the back of the gauges. Pulled the gauges today and wasn't even connected. D'oh. Reconnected the harness and worked perfect lol. I guess that should have been my first place to start before digging too far into any other wiring. Thank you again :)

 

-Jared