trailer brakes locking after new 7 way installed


New Member
Hello, we have a 21 ft dual axel travel trailer. Last winter we had our 7-way plug get corroded. What brought the corroded plug to our attention was that the brake controller inside the truck had the green light lit up when the trailer was not connected. My husband said that probably snow, salt or whatever got into the plug that caused the light to go on. Sure enough when he removed the plug a few months ago, we had a corroded plug. My husband replaced the 7-way plug and we are now having the trailer brakes lock up for about 10 feet and then release when we try to pull out of our driveway. It only seems to be the brake on the passenger side rear wheel. Previous to the replacement plug we did not have any problems. Any ideas as to what could be causing the rear wheel to lock. Do you think we have a bad new 7-way plug? We have not been able to use it this summer and now that it is fall, we are stating our field trial season and need to live in it for the next few weekends. Thanx in advance.


Senior Member
trailer brakes locking after new 7 way installed

Very odd. If it was all the brakes, and they stayed locked up, the culprit would almost certainly be the brake circuit is shorted to the 12 volt circuit. If it was all the brakes, and they only locked up when the brake pedal was depressed, then it would likely be the brake circuit is shorted to the brake light circuit.

I guess the first step is to isolate the problem to the trailer or the truck. The easiest way to do this is to buy or make a test rig which plugs into the 7 way socket. Watch the tester while backing the truck (only) out of the driveway, and see that all circuits (brake light, turn signals, taillight, (backup light if connected) and 12 volt (battery charging) connections are working properly, and the brake controller provides proportional voltage as brakes are attempted to be applied.

Next check that all the trailer brakes are working, not just the one which locks up. Easiest way to do this is jack up one side and pull the disconnect pin. All brakes should lock up; repeat to verify the other side.

This should isolate the problem to one or both of a bad (or miswired) plug and/or socket), and all but one of the brakes not working. If the cause is still unknown, it will probably require tracing wiring in the trailer to see how only 1 brake can be locking up.