Does Trailer Coupler Provide Adequate Ground for Trailer Lighting Functions

Updated 09/21/2017 | Published 09/20/2017

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Hook Probe Circuit Tester

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10 Gauge Wire - Blue Primary - Per Foot

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Trailer Wiring Junction Box

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Question:

I dont have a white wire. Does trailer need to be on ball of truck for it to work?

asked by: Lois M

Expert Reply:

Trailer wiring, whether 4-pole or 7-way, typically uses a white wire as ground. On a trailer this white ground wire would usually connect to a clean bare metal spot on the frame on one end and to a wiring junction box like # 38656 on the other end.

If the trailer lights work only when the trailer is coupled to the hitch ball then this tells us that this mechanical connection between the coupler and ball is making a sort of temporary (but inadequate) ground connection between trailer and vehicle. Some or even all trailer lights may work under this circumstance but since the connection between the coupler and ball is not always consistent you could have the lights blinking on and off as you go over bumps in the road.

You can attach a 10-gauge wire, such as # 10-1-1, to the ground pin on your trailer connector and to the trailer frame (to a clean bare metal spot) to provide a suitable ground to ensure your lights and other trailer circuit operate properly.

expert reply by: Adam R