Troubleshooting 7-Way Trailer Wiring That Engages Trailer Brakes When Headlights Are Turned On

Question:

Ive put a 7 pin and new trailer hitch on my truck. All Lights work an Trailer. My issue is , when I turn on headlights , the trailer brakes lock up. Any Idea Why ??? Thanks in Advance.

asked by: Jesse

Helpful Expert Reply:

The issue you describe, your trailer's electric drum brakes engaging when you turn on the headlights on the tow vehicle, is likely to be a simple mis-wiring of the 7-way. If the trailer connector was very old the issue could be caused by internal corrosion in the connector that could be bridging together two different circuits, but with a brand new 7-way the problem is likely to be either a mis-wired 7-way socket on the vehicle or a mis-wired 7-way plug on the trailer.

If you refer to the linked article on trailer wiring you will see the different ways that a 7-way can be configured. On the common RV Standard wiring configuration the socket contact at the 11-o-clock position carries the running light signal while the contact opposite that at the 5-o-clock position carries the trailer brake signal. Just double-check your function/pin assignments on the trailer side to make sure it matches that on the vehicle socket.

expert reply by: Adam R