Troubleshooting Trailer Wiring Where the Stop/Turn Signal Functions but Not the Running Lights

Updated 06/09/2014 | Published 06/08/2014

Question:

99 Durango installed trailer light wiring according to directions grounded harness to truck frame. all running lights work, but no turn signals or brake lights on trailer signals and brake lights work at harness connection on truck side of harness - only running lights work on trailer side of harness. help?

asked by: Opie

Expert Reply:

You've narrowed down the problem to being somewhere on the wiring of your trailer. The first place to look is the trailer connector. Look for corrosion in or behind the connector, cut or exposed wire that could be shorting the circuits and fix as necessary.

The next place to look is the taillight assemblies themselves. Since both of them work with the lower illumination of the running lights but not with the brighter illumination of the stop/turn signal I suspect the problem is that the grounds of the assemblies are not strong enough to handle the amount of current required to illuminate the brighter portion of the bulb.

I attached an FAQ on 4-way installs and on trailer wiring for you to check out.

expert reply by: Jameson C