Is it Normal to Read 0.2 Volts at the Brake Magnets When Brakes Are Not Applied

Expert Reply:

The slight voltage you are seeing at the brake magnets is completely normal, and most likely does not indicate a problem.

Proportional brake controllers like the Tekonsha Prodigy you referenced send a minimal amount of voltage through the brake output circuit to confirm that there is a trailer connected. According to Tekonsha, the check voltage sent along the circuit is actually a pulse rather than a constant amount, but because the brake magnets can hold some of the voltage for a moment, the fact that the current is pulsing might not be easy to read with your voltmeter.

Just to rule out any possible problem, I would recommend closely examining the trailer connector plug and socket. Look for any green corrosion on the pins or sockets. If there is corrosion, sometimes it can spread to the interior of the connector and result in voltage bleeding from one of the terminals (like the 12-volt accessory circuit) to another. If all is well with the connectors, you are good to go.

expert reply by: Mike L