Troubleshooting Output Shorted No Brakes Message on Tekonsha P3 Brake Controller

Updated 06/30/2025 | Published 09/01/2017

Question:

I keep having intermittent service with my tandem axle brakes. I bought a Tekonsha P3 controller and also replaced both the truck and trailer connectors. I tested from the controller back to the truck connector and it tested fine so I am now turning to the trailer. The P3 gives me an Output Shorted No Brakes message. I found one broken wire and repaired it. I thought this would solve the problem and the message went away and brakes worked in the drive. Next weekend i checked them again and then got the error message again. Before i start working from hub to hub I have a question. If one magnet is shorted, will it affect the other 3 brakes too? It appears that none of the brakes are working so what is the likely problem?

asked by: Randy

Expert Reply:

It does sound like there is a possible short with the brake magnets on your trailer, especially if all the wiring looks good between the brake controller and vehicle connector.

I recommend first making sure that each magnet has one wire secured to the trailer frame for ground and the other is connected to the brake output circuit. Check that there are no damaged or exposed areas that might be making contact to the trailer frame. If the wires all check out, then you will want to test the magnets themselves.

I have attached an article on testing brake magnets that you might find helpful. To test an individual brake magnet for a short, you will want to touch the base of the magnet to the negative post of a 12-volt battery. Then connect one of the brake magnet wires to the negative lead of a multimeter like # PT89ZR, and the positive lead of the multimeter to the positive post of the battery. If you detect any amperage, the magnet is shorted and should be replaced.

If one magnet has a short, it will not directly affect the other assemblies, but it will cause issues back up at the 7-Way connector. This can in turn affect the other assemblies from working correctly. I have attached a link that will take you to our available selection of brake magnets if you find this is the problem.

expert reply by: Chris R