Troubleshooting No Display, Trailer Brakes, or Brake Lights When Using Prodigy Brake Controller  

The fact that the brake light is not working makes me think there is a ground problem which could also be the reason the trailer brakes are not working. The first thing I would check is the ground on the vehicle side 7-Way, the ground on the trailer, and the ground for the brake controller. Make sure they are mounted to a bare metal surface that is clean and free of corrosion. The lack of display on the brake controller could mean it is not receiving power or not receiving enough power. You will need to test the black wire on the back of the brake controller to be sure it is getting power. If it is not getting power, then new wiring to the brake controller may solve the problem. If it is getting power, but not sending it out along the blue wire, then there is most likely a problem with the internal circuitry of the brake controller and it will need to be replaced. If the display reads a lower dash, a period, and another lower dash, that indicates that the brake controller is not properly mounted. It could have been bumped at some point, and you may not have noticed between towing seasons. The solution is to mount the controller as explained in the instructions linked below. This would also mean that the brake light is a separate issue unrelated to the brake controller. The tester could be allowing the controller to register 10 because the brake controller does send some power back along the blue wire to check if a trailer is connected. So when the tester is connected, it might think there is a trailer connected and thus register a number. This makes me think the ground and/or other wiring on the trailer side is the culprit. Finally, the brake magnets may need replacing. Check them visually first. If the magnets show abnormal wear or if you can see the windings beginning to show through the friction surface of the magnet then they will need to be replaced. To further test your magnets, first make sure the trailer is not connected when performing this test. If the trailer is connected, you run the risk of shorting out a brake controller or various other electrical components. To test the brake magnets with an ammeter, connect the ammeter between the positive battery terminal of a separate battery and one of the magnet wires. Then, connect the other magnet wire to the negative battery terminal. Check the amperage, if the amperage is greater than the specified amount in the chart below, replace the magnet. If the reading is less than the specified amount, then the leads are bad and the magnet should be replaced. Electromagnet Specifications: 7 inch Diameter Brake Drum: Max Amps at 9-10.5 Volts 2 Brakes 4.7-5.6 4 Brakes 9.5-11 6 Brakes 14.3-16 Max Amps at 12-13 Volts 2 Brakes 6.3-6.8 4 Brakes 12.6-13.7 6 Brakes 19.0-20.6 10 and 12 Inch Brake Drums Max Amps at 9-10.5 Volts 2 Brakes 5.6-6.6 4 Brakes 11.3-13.3 6 Brakes 17.0-20.0 Max Amps at 12-13 Volts 2 Brakes 7.5-8.2 4 Brakes 15.0-16.3 6 Brakes 22.6-24.5 Next, disconnect the negative wire from the brake magnet wire and connect it to the base, housing, of the brake magnet. If there is any amperage, the magnet is shorted and will need to be replaced. Finally, using an ohmmeter, check the resistance between the brake magnet wires. If the resistance is not within the specified range below, the magnet will need to be replaced. 7 inch brake magnet resistance should be 3.8-4.0 Ohms 10 and 12 inch brake magnets resistance should be 3.2-3.5 Ohms If the magnets just need to be replaced, we carry various types and sizes of magnets. I have included a link to the ones we carry below. I have also included a video that shows, in part, replacing magnets. I have also included a link to the instructions for the Prodigy brake controller # 90185.