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Troubleshooting Turn Signal Malfunction on a 2004 Ford Escape Using a Modulite Wiring Harness


Installed Modulite HD 119190 ok I received it as a gift about a year ago, but installed only last month. All connections tested OK, and Output OK. after running the car for about two weeks, the turn signal circuit went bonkers. Car acted like it had a burned out light. Checked all lights, no burnouts. Finally needed to removed the Modulite completely from the car. All car turn signals are OK again! What is the problem?


Expert Reply:

When your lights are acting strangely, or stop working, what is most likely the problem is that you have a ground wire that is not connected as it should be or a short in the system.

With the # 119190 wiring harness connected, I would recommend checking the white ground wire to make sure that it is firmly connected to a clean piece of metal on the vehicle frame. Buildup, rust, and paint can all cause interference with the ground connection.

The best way to determine where the problem is actually starting would be to test the unit without your trailer connected. Use a circuit tester, part # 3808 if needed, to test the wires going into the black converter box, as well as each port on your 4-Way plug. It is easiest to have a friend in the cab engage the turn signals and brake pedal while you test each wire for power.

If you find that you have power on the wires going into the converter box, but not coming out, this would indicate an issue within the converter box unit, and would mean that the # 119190 would need to be replaced, as it is not user serviceable.

If you do find that you do see power moving correctly through the box to the 4-Way plug, I would recommend turning your attention to the trailer itself. Check the ground wire coming from your trailer connector to make sure there is nothing interfering with its connection to the trailer frame. You can also check your trailer lights to make sure each light is still functioning correctly and that there is no buildup, corrosion, or paint between the ground wire or light hardware.

I am providing a link to a video demonstrating how to test for a correct ground connection, if needed.

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