Left Turn Signal Makes Lights Flash and One tail Light Works when Connected to 2007 Ford Freestar  

Question:

Expert Reply:

It sounds like there is a ground and/or connection issue on the trailer or an issue inside the converter box on the vehicle but there are ways to determine if that is the case or if the harness for your 2007 Ford Freestar is the problem. First, disconnect the trailer from the vehicle. Then use a circuit tester, such as # PTW2993, to test the 4-Way connector while someone sits in the vehicle and operates the lighting functions.

If the 4-Way end does not have the right signals when testing then check the white ground wire and make sure it is attached to a clean bare metal surface with no paint or coating on it. Also check the connections to the vehicle for any bent or broken pins. If the problem persists then there is something wrong inside the converter and it will need to be replaced.

If everything on the vehicle side checks out then the issue is on the trailer. Sometimes the tow package on one vehicle can overcome corrosion or weak grounds better than other vehicles. Make sure that the trailer's connector is clean and free of corrosion. Corrosion build up could cause these issues.

A bad ground somewhere could also be the culprit. Ground problems normally show up when there is more draw on a system such as when you have the running lights on and then use another function like a turn signal or brake light but can show up any time.

The light grounds should also be attached to clean and corrosion free bare metal surfaces. If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.

expert reply by: Michael H

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