Diagnosing Popup Trailer Left Side Brake and Taillight Not Working with a 1999 Dodge Ram 1500 Truck

Expert Reply:

It sounds like you have a problem in the trailer wiring, as you have suggested, because the trailer brake power is getting to the right side brake assembly. I would start by checking the brake magnet wires for proper ground and power on the left side. We have a video, see link, that shows testing the brake magnet that should be helpful. Make sure to check the wiring all the way back to where the magnets are grounded and the power is spliced from the right side brake magnet that is working.

There is also a possibility that the brake magnet is bad. Inspect the magnet to see if there are windings showing through the contact surface or deep grooves in the surface. If so you would need to replace the magnet. Now would be a good time to check the brakes and contact surfaces on the trailer hub also.

If the magnet does not look bad, you can check its function. We have a detailed article showing how to test the brake magnet with a multimeter, # PT89ZR, see link.

For the left side tail light not working, I would check the tow package fuses in the power distribution box under the hood first, since replacing the bulb on the trailer did not help. You should also check the wiring in the trailer connectors and make sure the left side light is properly grounded to the trailer frame.