M1102 wiring issues RESOLVED

[DK84]

I have recently purchased an M1102 trailer and spent sometime converting the wiring over to 12v.

I have a 2017 Police Interceptor SUV with a 7-pin connector. I know my rig wring is sound; I had no issues using temporary towing lights when I picked up the trailer. I installed a 7-way junction box that terminals all the connections from my car. I then connected the 4 needed circuits to the trailer wiring loom (running lights, left brake/blinker, right brake/blinker, and earth). I made a new earth connection directly into the chassis and confirmed connectivity. I changed the 24v bulbs in the tail lights to compatible 12v bulbs.

However, when I did my first light test, nothing worked correctly. When I turn my car lights on, nothing lights up on the trailer. Left blinker, nothing, brakes and right blinker, all the lights come on. As cool as flashing running lights are, it isn't legal or usable on the street. Thinking it was an earth issue, I confirmed the new earth connection; it has connectivity between the earth loop on the trailer, the chassis and my car earth. I then checked every earth connection on each of the lights - they all have connectivity.

I have triple checked my connections within both the junction box and to the trailer wiring loom.

I'm at a loss as to what else to check or what the problem could be. Has anyone else seen issues like this and found root cause? Are there any other earth connections within the wiring loom, other than the main earth stud and at each light? Thank you.

 

[Jeepadict]

There's a ground connection at the forward crossmember you may have missed in your junction box.

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[DK84]

Is that the same connection as the original ground stud? A bolt with a circle connector near the brackets that hold the

 

[Jeepadict]

Yup

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[DK84]

SITREP:

I spent a couple of hours working on the trailer today and discovered the issue - which was really easy to fix. So that others can learn from this thread let me outline my diagnostics.

I wanted to determine if there was a problem within the wiring loom itself or a light module. I removed all the running light LED modules and all four rear bulbs. I thought that maybe a running light had failed and was causing a short to earth. As I was removing the running light modules, I was measuring the resistance between the pins to find one that was way off from the others, indicating a fault. For reference, working modules have an open circuit connection between the pins. All of my running light modules had the same pin-to-pin resistance.

With all the LEDs and bulbs removed, I checked connectivity between the three circuits. As expected, there was no connectivity between the positive lines of the three circuits. I then checked that there was a solid connection between my junction box and sockets on each of the circuits. The three connections were also good.

Now I've proved there are no shorts between the three circuits, my connections within the junction box are good and none of the running light modules are at fault. This left the cable from the car to the junction box. I purchased this from Amazon so was not expecting any issue with the cable. But...

I checked continuity from the left tail light in the junction box and the plug. The center pin (7) beeped, when it should have been the right middle pin (5). Hmm, something was wrong. I quickly disconnected the four wires in the junction box, isolating the cable from the trailer wiring loom. After toning out each connection and checking the pins on the plug I discovered two issues: the left taillight was indeed connected to the backup light pin and the running light connection was connected to the aux 12v pin. I confirmed that ground was properly connected. Now that I knew the plug had cross connections, I had to rewire my junction box to correct the errors in the cable. The junction box looks wrong, but all the lights on the trailer now was as expected.

The lesson, ALWAYS check your cables. There was nothing wrong with the light modules on the trailer or the wiring loom. Had I checked the cable when I first received it, I would have confirmed the cross connected pins, putting the corrections in the junction box as I installed it there would have been no issues.