7-pin Wiring Issue/Question

[jjohnson1892]

Hey everyone,

Having an issue with lighting for my XV-3. I installed the Mopar 7-pin wiring harness on my JKU last night, and the trailer's lighting didn't work properly. Here's what is happening:

-When my Jeep's lights are on, the trailer lights do not function (brakes, indicator, running lights)
-When my Jeep's lights are off, the trailer lights do function


This was a bit of a bummer when trying to prep for a trip next week (VOR). My uncle went over with his JKU w/ 7 pin wiring, and the trailer lights functioned properly. I believe it has also worked with another vehicle (Ford F250), but not confirmed.

Now that I know the issue likely lies with my Jeep's wiring, any ideas on where to start? I will be troubleshooting after work, but we followed the install instructions by the book for wiring.

 

[Weeds]

With all trailer lighting problems, first check your ground connection. I also spray the trailer to jeep plug with a electromotive cleaner, available in in auto store. As strange as it may sound check all turn signal bulbs in the jeep for moisture and corrosion. Good Luck.

You should post this question in the trailer thread.

 

[jacobconroy]

I'm not sure about the Jeep, but this is the diagram that I have used for all my rigs (so they match):


Hasn't lead me wrong yet. To the best of my knowledge...the above trailer plug configuration is considered "standard". I would get a test light and test each pin on the vehicle side.

If that all checks out...do the same checks on the trailer side. This will probably be more complicated.

It's possible that the light circuit in your Jeep is working with a relay that uses a ground connection to turn on the lights (instead of a +12 volt signal...like older cars). If this is the case, things can become labor intensive. Would involve another inverse-polarity relay to change it back to a positive switch. Just a guess though.

In any case, I would start by verifying all the pins in the plugs. Good luck dude!

 

[chet6.7]

 

[jjohnson1892]

Thanks for the suggestions everyone - I haven't had time to get around to this, but will update when I do get time.

 

[1stDeuce]

Yup, bad/no ground is very likely.
I think the 7 pin JK harness is completely plug and play, with no dangling ground wire that you need to screw to the chassis, so it is very likely that your problem is on the trailer side unless you got a bad harness.

Check to see if the ground pin of the vehicle 7-way connector has continuity to ground. If it does, check the trailer. One or the other is not grounded properly. It is possible that the trailer lighting is also not grounded to the trailer chassis, so you may have to visually look at the ground wire to see if it is populated to the trailer lighting... With LED lights, I'm not sure you can just check resistance between the ground and taillight circuit, for example...

 

[dstock]

Yup, bad/no ground is very likely.
I think the 7 pin JK harness is completely plug and play, with no dangling ground wire that you need to screw to the chassis, so it is very likely that your problem is on the trailer side unless you got a bad harness.

Check to see if the ground pin of the vehicle 7-way connector has continuity to ground. If it does, check the trailer. One or the other is not grounded properly. It is possible that the trailer lighting is also not grounded to the trailer chassis, so you may have to visually look at the ground wire to see if it is populated to the trailer lighting... With LED lights, I'm not sure you can just check resistance between the ground and taillight circuit, for example...

Actually, that's not entirely correct as it's not completely plug and play. You do have to connect separate power and ground to the battery and connect the brake controller wire if you are using a brake controller.

 

[1stDeuce]

Good point. I knew about the battery connection, just wasn't thinking about it. If there is a ground wire to connect, the OP may want to double check that it's properly grounded, not to a bolt that only goes to plastic.

 

[jacobconroy]

When I was a younger pup I managed a small stereo shop doing 12 volt work and then progressed to wiring up cop cars, fire trucks, search and rescue rigs, ambulances, etc.

This doesn't make me any sort of expert, but I can tell you that just about every trailer wiring setup I've seen (both private and "professional") has had corners cut. The biggest culprit is ground wires. The second culprit is the lack of fuses when folks tap into factory wiring for brake signals, turn signals, and backup lights.

Folks will install a 7-pin plug in their rig and either screw or bolt the ground wire to the frame (right next to the rear bumper). This in itself isn't so bad...but they usually won't clean the paint and/or corrosion off the attachment point with a grinder first, nor use a star washer to "bite" into the frame. They never coat the attachment point with something that will prevent corrosion.

My best advice is to spend the money and take the time to run two heavy gage wires (like 8 gage or heavier each) to the battery of the tow vehicle for 12 volt and ground, plus the brake wire of at least 12 gage. All the way from the 7-pin jack on the rig's rear bumper to the battery. Lotsa dirty work.

The ground connection in any 12 volt setup is EXACTLY as important as the 12 volt power supply wire. The ground wire needs to be the same gage as the 12 volt supply wire too...and sometimes the ground wire needs to be a heavier gage if it is supporting the 12 volt supply, plus two turn signal circuits, plus backup lights.