I was ask to look at a trailer on the left side tail lights the inside and the marker on the out side corner were flashing on and off but the other tail light was ok. It is something in the pig tail that gos throw the hole in the L side tail light box because if you moved it around it would go on and off. On the back of the trailer is a juncstion box were there is a cord from the L Side TL that looked like it only had 3 wires in it. When it gets to the TL box its got a big molded on rubber end with maybe 10 wires comeing out of it. I ran a wire from the juncstion box to the end side light and the marker light to get it working while i find a new harness. It had been a hard day and i was at the end of my rope but i couldnt see a ground wire is this one of those deals were it ground throw a wire that does something else?
Most of the factory harnesses are molded units. Where the main harness splits usually there is a place for a mounting bolt with an eyelet built in. That is the ground and on the right and left harnesses it will use the same mounting/ground set-up. Truck Shop
It has a L and R harness but it didnt have any way to bolt it down. I had another guy look at it that has messed with alot of wireing and he didnt see a ground ether i will get a better look at it when i get a new one.