Troubleshooting Trailer Brakes Locking Up When Connected to Truck

Question:

My friend has a 1979 dodge p/u and when he plugs the trailer to the truck the brakes on the trailer set up! Unplug the trailer and the brakes release! He said he towed it here to our location several hundred miles just fine! The truck battery discharged due to not unplugging the trailer and this is when the problem arose. Any ideas?

asked by: Ron G

Expert Reply:

It sounds like there is some corrosion that has built up on the trailer connector causing that 5 o'clock brake output pin to have constant 12V power. I recommend cleaning the connections on both the vehicle and trailer side with some sand paper or steel wool and then using some dielectric grease like # 11755 to keep debris and moisture out of the connections.

You can use a circuit tester like # PTW2993 to test the pins for function and also test the breakaway system for function.

If he wants to ensure the truck battery doesn't discharge in the future, he can simply use the Battery Isolation Solenoid # PK5231201 so the truck battery won't drain when the truck doesn't have the accessory on.

expert reply by: Jason S