Troubleshooting Possible Poor Trailer Ground Causing Trailer Lamps to Flash

Question:

When I plug the 7 pin plug in to back of truck all lights work on there own like indicator work fine side lights work fine and brake is fine but if you have indicator on and apply the brakes everything starts flashing or if lights are on and you apply indicator same happens again any ideas thanks

asked by: Dean

Expert Reply:

What you describe is a classic symptom of a poor ground. On the tow vehicle, make sure the trailer connector is grounded to the tow vehicle frame. On the trailer side, the trailer connector white wire should be securely grounded to the trailer frame using a ring terminal and a self tapping screw. If this connection is loose or corroded, it'll prevent a good ground connection. Make sure each lamp is grounded. Trailer lamps will get their ground connection either by the mounting studs being in direct contact with the trailer frame or by a dedicated ground wire connected to the frame.

Another possibility.... If the tow vehicle has a 'bulb out' sensor that causes the turn signals to rapidly flash when there's a bulb out, trailers with LED lamps won't pull enough voltage and the sensor thinks there's a burned out bulb. If that's the case, installing load resistors like # DI34ZR on the turn signal/brake lamp circuits will cure the problem.

I'll link you to some trailer wiring articles that you'll find helpful.

expert reply by: Mike L