Troubleshooting Trailer Lights Not Working

Question:

This problem started when I hooked my 1993 Stratos Boat trailer to my 1500 GMC and had no lights on the trailer. I found a loose ground for the left rear light and repaired it. The blinkers now work but the other lights are not working. I recently used a Uhaul trailer and all the lights worked when I rented it. When I returned it only the blinkers were working just like the boat. Any suggestions??

asked by: Bobby P

Expert Reply:

As you found out, in most cases a bad ground is to blame for this type of issue, and I would still be on the lookout for that. There are other steps you can take as well to try and determine the specific problem; you'll need to use a circuit tester such as # PTW2993 to test the connector on your vehicle after disconnecting it from your trailer. Check the wiring going into your harness from your taillights to see if those wires are carrying the correct signals, which they likely are since the issue seems to be on one trailer only. If the signals going to your harness are okay, you'll need to test the signals coming out of the harness, and if they are correct then your issue is likely going to be with the trailer side wiring.

As I mentioned above, an important issue you still want to take a look at are the ground connections, as they can be the cause of numerous lighting problems. You'll want to make sure your grounds are securely attached to bare metal surfaces free of any paint, dirt or corrosion of any kind. Also check your wiring thoroughly to ensure there are none that are crimped, broken or otherwise damaged. I've added links to a pair of help articles on trailer wiring that you may also find useful.

expert reply by: Kyle S