Troubleshooting Electric Trailer Brakes Humming When Connected To Vehicle Wiring

Published 12/30/2022

Question:

With trailer unhooked should and pins in plug have voltage on them. When you hook up trailer to truck open circuit come on but brakes humm. When you let off brakes it goes to p3 screen

asked by: Danny W

Expert Reply:

Typically you will not see any voltage on the trailer side of the connector. The 12-volt charge line circuit is generally the only one which will have power depending on if there are diodes in the wiring to prevent power from flowing back through the trailer battery.

The vehicle side connector will have power on the different circuits without a trailer connected. This is generally not an issue as they will require a ground connection to complete the circuit.

With your brakes humming when you connect your truck and trailer it sounds like you have a short in the brake line wiring. This short could be on the truck or trailer side. If your Prodigy P3 # 90195 acts like a trailer is connected when one is not the issue is on the truck side. If it is showing no trailer connected when disconnected the short is on the trailer side. You will need to trace the wiring and check any connections to determine where the short is located.

expert reply by: Bud M