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Trailer Light Problem

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Okay so I've recently spliced in a flat 4 trailer harness in preparation to pulling a trailer I am going to be picking up. I found the write up on here which is:


"After searching the forums is became apparent that there is a lack of information on wiring trailer harnesses to the MJ. Although it would be nice to get one of those 'plug and play' type kits that are available for the newer vehicles, they are in very short supply for the 86-92 trucks we drive (at least down here).


Jeepcomj had a great idea in one of his posts, go to the junkyard and get the under body to stop/turn/parking light harness connector (both sides), leaving enough loose wires to create your own 'plug and play' set, but that still does not address our hook-up problem...so:


The rear stop/turn/parking harness has 5 actual wires in it, and although there are numerous factory splices to duplicate wires to each of the plugs, the wire codes are as follows:


Brown: Right turn and brake light

Black: Ground

Blue: Tail (parking) lights

Brown with white tracer: Backup light

Grey with black tracer: Left turn and brake light


Another way to explain it: Assuming you are standing at the the back of the truck, the LEFT side being the drivers side, and the RIGHT side being the passenger side, the main body ground will be behind the left tail light, and the plugs on the left side will have the gray w/ blk tracer wire. The right side will have the brown wire.


To hook up a six pole receiver you have six wires:


White: Ground (Don't ask why...)

Brown: Tail (parking)

Yellow: Left Turn

Green: Right turn

Blue: Electric trailer brake

Red: Auxillary



Harness TO Receiver:


Brown TO Green

Blue TO Brown

Black TO White

Brown w/white TO Red (my choice - my trailer has reverse lights)

Grey w/black TO Yellow


For a 4 wire flat connection it would be:


Harness TO Flat 4:


Brown TO Green (sometimes with yellow tracer)

Blue TO Brown

Black TO White

Grey w/ black TO Yellow



Hope this helps!



And I did exactly what it says. What's happening is, the turn signals, both sides are working for the harness I spliced in, and the flashers work as well, and also when the brake is depressed. But when I pull the knob to turn on headlamps/taillights the turn signals, and flashers stop working properly for the harness, but all lights on the comanche are working properly. Did I hook it up wrong, a fuse has blown, or a bad ground?

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You need a HD flasher..........yours will NOT power the additional  lights.



Mine won't work with the trailer plugged in either.....but I don't care.



From what I gather from your post....all works BUT the flashers with lights on....correct?

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I'll clean up the grounding behind the drivers side tail light.


And jeep driver yeah. the flashers, turn signals and brake lights for the trailer work when the running tail lights aren't on. But when I pull the knob as if to drive at night to turn on running taillights the flashers, turn signals, and brake lights for the trailer don't work. the running taillights will turn on though.

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So you don't have a trailer to plug into?


Are you using a borrowed trailer to test?


Are you assuming that the borrowed trailer is wired correctly?


Is the harness on both sides grounded well?


Did you clean the ground at the rear yet?





When you get YOUR trailer......take it step by step......every connection....or splice.........all the way to the trailer lights and test each wire.


Might even consider rewiring your trailer.



I'm going to rewire mine AGAIN, this time I'm using a 50' 16g extension cord. Will have three wires, turn/brake, running, ground. The trailer wire will wear and ground out after a while, the extension cord will be a lot tougher.

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Also, if you are using a borrowed trailer, know that most trailer lights are $#!&. Sockets corrode, ground out......just simply fail. And that in and of itself may be your problem.


If you can swing it, get a pair of sealed LED lights........yeah......like $50 for the pair........really like mine, nice and bright.

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The person I'm buying from bought the trailer new and it's been a garage, he's never even pulled it out to use. So hopefully it's in decent condition. I'll get back to this post after I get the trailer tomorrow

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12V magnetic base trailer lights - These might be of interest after/while wiring your truck - - Been around for some time - Bought mine at least 10 yr ago - easy enuff to zip tie/clamp/magnet or whatever where ever & then afterwards back on the shelf & ready for the next time - - - Sold many places - - Amazon-eBay-Northern & routinely Harbor freight sale/special item $9.99 





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  • 3 months later...

Hello.  I have a question on this topic... what driver's side rear ground?  I own a 1988 Comanche Pioneer and I towed for the first time recently.  I went to Advanced Auto and cut the old wire harness and soldiered/ taped the new wire harness together.  I helped a buddy move his lawn mower in the rain and I noticed my dashboard lights were not working.  Today, in the daylight I pulled the fuse and it was burnt to a point of a serious concern.  The dimmer and door chime10-amp fuse had a burnt hole through it.  It is funny as my gauges worked but when I put a new fuse to replace the burnt fuse, my gauges no longer worked, I merely put back the same 7.5 fuse (because I did not have another one) and my gauges illuminated again.  But when I drove the truck up my driveway and turned on the radio, the truck almost stalled.  When I went to go start it again it only clicked, but when I turned on the radio and tried to start it again- it started right up.


I seem to have some sort of electrical issues now, when before I never had ANY issue with this truck since I bought it- it always worked perfectly.  Was I supposed to ground something?  I just figured the ground wire was already set when I soldiered them. In studying the manual it mentions a 30 amp-towing fuse, which I do not have in place.  Should that 30-amp fuse be in there?  Any ideas on what is going on?  Did I just mess up my truck?


I am a bit confused and a bit worried now.


Thanks very much, your website has a ton of knowledge.



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