Trailer running lights on 2012 JKU not working

bobholthaus

Observer
The trailer running light circuit on my 2012 JKU isn't working; I tested the lights on my Grand Cherokee and it's not the trailer. Brake light circuit works fine, as do all of the other circuits in the oem 7-pin connector. I called my dealer and she looked up that the circuit is tied to the license plate light, and sure enough, it's out. She told me to check fuse M13 and M16, and both are fine. I just tested every fuse in the box, and all are fine. Interesting that the "left horn" and the "rear wiper" fuses don't have power to either side when the vehicle is running. Checked at the oem harness and there is no power to the pin; also checked the license plate bulb, which showed signs of corrosion, and there is no power there either. I will take left taillight out tomorrow night and see what I find; I know the oem 7 way harness plugs in behind that taillight, which is working fine. There IS a fuse by the battery that is part of the oem 7-way harness, but that one feeds 12v to the main 12v feed in the harness (the one that charges the house battery on my trailer, for instance; that fuse has nothing to do with the running lights (which has been mentioned in some other older posts; that fuse is fine and IS powering the 12v pin in the harness)). Anyone have any idea how to fix this? I'm totally stumped, and 12v wiring is my specialty. Thanks.

I feel like this happened one other time in my Wrangler and the dealer had to reset something with their starscan tool; I will look back in my service records to see if I can find it. As I'm no longer under warranty, I'm trying to prevent a trip to the dealer!


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unkamonkey

Explorer
Check the wire from the trailer plug to the socket and check both ends. Corrosion happens at either end. We used to travel with a points file for a reason. When ever I have to plug anything in on the back of a vehicle, I check the lights, I have to wiggle the plug around to get things to work sometimes.
 

14JKURX

Observer
Check all of your grounding connections.
Grounds or the lack of cause more problems than power connections.
 

bobholthaus

Observer
I plugged the trailer back into my Grand Cherokee today and the lights are fine. I believe that this is an electrical gremlin that might be related to the CANBUS of the Wrangler. I will keep you guys posted. Thank you for the suggestions!
 

bobholthaus

Observer
On your advice I took all of the ground wires off of the negative terminal and added more dielectric grease to them all; there are no visible signs of corrosion, but my brake controller was flashing a "losing ground" error last week as well, and its grounded at the same location as the 7-way OEM trailer harness. Unfortunately, the grease didn't help.

I did take apart the license plate bulb socket and realized it was so corroded that the contacts broke off; I've had that license plate in muddy water before, which is the culprit. So I took the mount apart and found that there is a 6" pigtail that connects to the vehicle wiring; hopefully I can get that pigtail without needing to buy the entire license plate holder assembly. I did test the power at the vehicle side Deutsch looking plug and there is power there; as I've read that the trailer running circuit is directly tied to the license plate lamp, could it may not be working because there's no bulb completing the circuit there?

I also looked at all of the plugs that come with the OEM 7-way and there's no signs of chafing anywhere; as they're all waterproof, I did not take them apart, which I will do next after I get this license bulb taken care of. As I'm pretty sure this happened once before, I still need to look at my scanned receipts and see if I can find a "reset" order of some sort; I still feel like they need to reset something in the CANBUS.

Btw here's the Manual to the harness I'm dealing with, which is Mopar® Part 82210214AB:

https://www.quadratec.com/sites/default/files/installation_instructions/75397.pdf

The part can be seen at:
https://www.quadratec.com/products/92015_111.htm
 

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