Left Side Brake and Turn Signals Not Working on Boat Trailer

Updated 08/05/2015 | Published 08/04/2015

Question:

I have running lights on entire boat trailer. I have no break and turn light on left side only. Installation professionally done by qualified master mechanic. Left light quit working. removed cover and noted 1157 bulb black. Changed bulb and left assembly was working. Any ideas?

asked by: Tom A

Expert Reply:

Sounds like changing the bulb solved the problem. If not, the first thing I recommend is checking the fuses in the vehicle to see if they will need to be replaced.

If the fuses check out it sounds like it could be a ground problem. A loose, broken, or corroded ground connection can cause all sorts of unwanted problems for electrical components including trailer taillights.

I would start with checking for a proper ground at the taillight itself. Trailer tail lights can be grounded in one of two ways. The first way is the tail light assemblies can be grounded by a separate wire coming out of the back of the tail light and attached to the trailers frame. The second way is the tail lamp assembly is grounded through the mounting bolt that attaches the tail light to the frame.

You will also want to check the ground at the front of the trailer for any dirt or corrosion. Finally, check to make sure the actual connectors on both the truck and trailer are clean and free of corrosion. A bad ground or dirty connections are the two most common causes of lights not functioning properly.

I am including a link to a video on troubleshooting the ground wire that should help and a link to a FAQ page on trailer wiring.

expert reply by: Chris O