All Trailer Lights Work Except for Brake Lights Towed by a 2004 Jeep Grand Cherokee

Question:

I have a 2004 Jeep Grand Cherokee with factory trailer wiring coupler. Everything park,hazzard,turn signals work but no power to vechicle harness when I apply brakes? Do I need to install something in the vechicle for brake lights for trailerNOTE: only need brake lights for boat trailer-trailer does not have brakes or maybe there is a relay that is bad?

asked by: Joseph G

Expert Reply:

Trailers in the US have combined brake lights and turn signals meaning the brake light signals and turn signals are sent on the same wire, one on each side. Since the turn signals are working that indicates to me that you potentially have a blown stop light of CHMSL fuse (CHMSL stands for center high mount stop lamp).

It could also be a fuse or relay associated with the tow package wiring. You will need to use the vehicle owners manual to find the fuse and/or relay locations for the stop light/CHMSL fuses and all tow package fuses and relays to check them.

The easiest way to check for a bad relay, if equipped, is to use a known good relay in place of a potential bad one. I have included a link to the right that will also help.

expert reply by: Michael H