A Plea for Help- Trailer Lights

[Steve Ericsson]

Excellent result!! Seems most trailer light issues come down to bad grounds somewhere in the chain.

[Steve Ericsson]

Also, check your hitch to receiver connection, make sure that it isn't too rusty or if your hitch is new, scrape the powder coating/paint off where it contacts the receiver. With a flat four plug, your ground is established through your hitch in most cases. Flat four you have left turn, right turn, tail and brake but no ground through the connector. Had this issue a few times with new hitches or rusty hitches that wouldn't make good contact anymore.

I disagree with what you have written above. Flat four has ground, running, left and right. Both left and right are energized for brake.

I'm sure your right, that's how it's supposed to be, mine originally wasn't that way. I discovered it when my lights flickered over every bump. I suspect it was the wiring harness kit I got for my old truck, it had a T that plugged into the tail light connector. For some reason the white wire wasn't grounded, when I got home that night I rewired it through the connector. Soon after I changed over to a round 6 wire connector so I could have back up lights on the trailer, it is really nice in the dark to see where I'm backing. My new truck is round 7, so I've gone that route on all my trailers.

If you Google "Trailer wiring grounded through frame", you'll find it's a common issue. It makes no sense and why they do it is beyond me. One more thing to check if you have trailer light issues, easy enough to check by plugging in your light without hitching up the trailer.