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Troubleshooting Electric Lockout on Trailer with Surge Coupler

Question:

Driving a 2018 Silverado 3500HD. My surge brake system trailer has a 5 flat lead and I connect it to my truck with a adapter that goes to a 7 round electrical receiver on the truck. Usually I have no problem going in reverse, but lately the trailer brakes have begun locking up. Ive tried two different adapters and two different vehicles, so Im thinking its a trailer problem, but I dont see any breaks or problems with the trailer wiring. Any thoughts.

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Expert Reply:

Your description of your trailer setup indicates that your surge coupler has an electric lockout feature to allow you to reverse the trailer without the surge brakes engaging. Some surge couplers use a manual lockout but yours has a solenoid with two wires (ground and hot) that take in the truck's reverse light signal; this closes the solenoid so no hydraulic brake fluid pressure can reach your brakes when you back up. Somewhere in your wiring you are losing your connection to the Silverado's reverse light signal.

If you have a circuit tester like # PTW2992 or # 40376 you can test the reverse light circuit's pin on the truck's 7-way. Ground the tester to the ground pin at the 7:00 position and probe the center contact which carries the reverse light circuit (please see the linked photo for guidance). If you detect the signal there then install your adapter and test its output end for the same signal. Keep testing as you move downstream toward the trailer to find the point where the reverse light signal is lost.

If you have the signal all the way to the trailer then you may have a bad solenoid. You can try applying direct 12V power to the solenoid using a fully-charged battery. The the lockout does not function then you need to replace it with # T4748800 or # DM11993.

If you need a new adapter please refer to the other linked page.

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