Troubleshooting Intermittent Running Lights On a Trailer with 4-Way Connector

Question:

my trailers running lights inevitably go dark after random period of time, but re-light with a tap of the brakes. im using a modulite with a flat 4 connection.

asked by: patrick m

Expert Reply:

The first things I would check are the ground connections on the trailer. The connection of the trailer lights to the frame is especially suspect if the lights get their ground through the mounting hardware.

If all of your ground connections are good and this does not solve the problem, I would next test the Modulite converter. Use a circuit tester, item # PTW2993 if needed, and check the wiring on the vehicle side of the converter. You should have power for each function, yellow/left turn, green right turn, red brake lights, brown running lights and black power from the vehicle battery. If any of these functions are not functioning properly then the connector or the vehicle wiring needs to be checked. If all of the functions going into the converter are good then check the trailer side of the converter and you should get power on the brown wire for the running lights, yellow should be the left turn/brake and green should right turn/brake.

If the converter does not show a problem then you should check the trailer for a broken, pinched or exposed wire on the running light circuit. If this is the problem, when the wire makes connection to the trailer frame the taillights are going out and by applying the brakes the wire is somehow moved and the short is broken.

expert reply by: Robert G