Troubleshooting Tail Lights That Do Not Work When Brake and Turn Lights Do Work

Question:

brake and turn lights work but not tail lights

asked by: Will

Expert Reply:

Most of the time when trailer brake and turn lights work but the running or tail lights do not work the cause is a weak ground connection on either the vehicle wiring harness or on the trailer. Stop and turn lights are on only for short periods while a tail light remains on continuously. This means it will draw more current and will be the light that causes a bad ground to show up.

The easiest remedy is to disconnect the ground wires on both vehicle and trailer and to re-install them after cleaning/sanding that grounding point to remove any rust, oxidation, primer, paint or grease that could be interfering with the ground. An application of dielectric grease like # 11755 will help keep those new clean connections from developing corrosion in the future.

expert reply by: Adam R