Trailer lights Not Functioning Properly Right Turn Signal Works But Not Brake Light

Question:

My left side lights will show turn/brake/flashers but no running light.. The right side has the running light and turn signals…NO brake light?? What could cause them to be opposite like this?

asked by: Aaron M

Expert Reply:

You do have a very strange situation on your trailer lights. It sounds like you have a combination of damaged wires and possibly a faulty converter on your vehicle that sends power to the 4-way connector.

The running light not working on the left tail light but it works on the right is a sign that either the filament for the running light portion of that bulb is bad or you have a damaged wire going to the tail light. You can check the bulb by swapping them since you know that you have one bulb that is working properly. You can also use a Test Light # PTW2993, to test along the wiring to determine if you have power going to the tail light. If you have LED's or you determine that your bulb is fine and the wiring is also good then the tail light assembly itself is bad and needs replaced.

For the right side tail light working and brake light not, this indicates to me that the converter inside the vehicle is bad as the power for both of these is sent on the same wire. You should use the same tester to verify this at your vehicle connector.

I have also linked some articles below on the lighting connections and troubleshooting different scenarios as an additional resource. And you can always reach out to me if you need any additional help.

expert reply by: Bud M