Replacing 4-Pole Trailer Connector on Trailer With 7 Different Circuits Feeding It

Question:

This is a weird one. I’m replacing the connector for my old trailer since it’s corroded and all. The old connector is a flat 4-pin connector with 7 wires leading to it. In order the wires are: Green Green/black Yellow Yellow/black White White/black White Before I test each wire with a battery, is there any clue as to which color is which. My assumption is green/black and yellow/black are tail lights, green and yellow are signal/brakes, and the 3 white are ground? Have you seen anything like this?

asked by: Cory

Expert Reply:

It sounds like you've got a pretty good handle on what you're dealing with. You're correct, the green is right turn/brake, yellow is left turn/brake, black/green is right taillight and black/yellow is left taillight. The remaining wires are almost certainly grounds. I'm guessing you're not the original owner of the trailer or the person who wired it last time.

Rather than grounding each trailer lamp directly to the trailer frame by its mounting studs or individual ground wires connected to the trailer frame and using the trailer frame as a ground wire, it sounds like somebody ran a ground wire from each fixture to the trailer connector. I'd recommend you ground the white wire from the trailer connector to the trailer frame, along with each ground circuit from the lamps on the rear of the trailer using a ring terminal on the end of the wires and a self tapping screw to secure them to the trailer frame. That way, you have a continuous ground but are also using the trailer frame as a ground connection in case any of the individual ground circuits should fail.

I'll also link you to some of our informational articles about trailer wiring. I hope you'll find them helpful.

expert reply by: Mike L