Troubleshooting Trailer Clearance/Side Marker Lights Working On One Trailer But Not Another

Published 09/02/2021

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Question:

Why is it I can hook to one trailer and have all lights work and hook to another and have no side markers or clearance lights?

asked by: Brian

Expert Reply:

There are a few different things that can cause the trailer side marker and clearance lights on one trailer to work when hooked up to your tow vehicle, but a different trailers lights don't work.

The easiest and first thing to check is that the trailer side connector does not have any corrosion or debris causing the connector to not make a good connection to your vehicle connector.

If no corrosion or debris is found then you will want to double check that the main ground on the tongue of your trailer is securely connected and has not come loose. The clearance and side marker lights come on with the running lights and since that is when all of the lights are trying to turn on at once, a bad ground can cause some to not work. This explains why only the clearance lights aren't working.

Next would be checking that you are getting power from the vehicle connector to the clearance lights. Using a circuit tester like # PTW2993 will tell you if you have a wiring issue causing power to not make it to the lights.

I went ahead and included a link to a helpful article on wiring, and if you can tell me exactly what you find I would be happy to go over more in-depth troubleshooting if needed.

expert reply by: Samuel C