Testing Trailer Lights

If you have electric brakes you should have a breakaway battery on your trailer. With this battery it's very easy to rig a test gizmo for your lights and brakes.

I bought an extra truck end for the trailer cord that I can plug into the trailer cord when the trailer is parked away from the truck. This extra has all the terminals for the trailer wires, including the trailer battery.

I attached a wire with alligator clip to the battery terminal on the extra truck plug. This alligator clip is hot when plugged into the trailer cord.

Each of the terminals on the extra plug are labeled. So to check the lights or brakes, all I need to do is attach the alligator clip to the proper terminal. I put a piece of tape over the ground terminal so as not to accidently create a direct short.

If you look close, you can see a PS scratched on the plug. That terminal is the Passenger Side brake/turn.

You might also see 'brake' scratched at one of the terminals. This can be used with a helper to energize the brakes while I spin a wheel jacked up off the ground. I like to do this in each direction for each wheel to make sure the electric brakes are in order before a long road trip.


A quick check of the trailer lights can also be done by using the key fob to lock the truck while standing behnd the trailer. However, this does not test both the running and stop/turn lights.