Troubleshooting Trailer Lights Not Working

Question:

Neither the left turn indicator nor the left brake light of either of my trailers work any longer - flat 4. The right brake and turn indicator work as do all the running lights. The vehicle is a 2005 Toyota Sienna LE. The trailer wiring harness has been working properly for at least 10 years. It is a plug no splice wiring harness specifically for this vehicle. How do I check out that the vehicle converter is working correctly? The vehicle voltage at the flat 4 seems correct: continuous at the brown lead with the running lights on. Voltage pulses appropriately when the respective turn indicator is on yellow or green leads and both pulse at the green and yellow leads when the 4 way flashers are on. With the vehicle off, the resistance ohms between ground white and: brown is zero yellow is zero green is infinite Any suggestions?

asked by: Paul

Expert Reply:

In order to troubleshoot the left side of your trailer's lights not working you'll need to use a circuit tester such as # PTW2993 to test the connector on your '05 Sienna 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, if not then the issue is with the vehicle wiring. 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.

An important issue you will want to take a look at are the ground connections, as they can be the cause of numerous lighting problems such as what you are experiencing. 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