Trailer Brake and Turn Signals are Not Working but Running Lights Work  

Question:

Expert Reply:

If you are using an adapter like # 37385, it could be that the adapter is not pinned out the same way as your trailer requires. What you can do is test the functions on the trailer connector on your vehicle with a circuit tester like # PTW2993 if needed to make sure that all of them are working properly. If they are then you know the problem is behind the vehicle side connector.

If they are not working properly on the tow vehicle it could still be a blown fuse or relays that needs to be replaced. You will need to consult the vehicle owner's manual to determine the location of any fuses/relays associated with the trailer connector.

Next, if you are using an adapter, plug it in and then test to see if all of the functions are working properly coming through the adapter. If they are not then there must be a problem in the adpater. If they are working then make sure that your boat trailer 4 or 5-Way connector is pinned the same way as the adapter requires.

If there is a difference then you will need to either re-pin the adapter, if possible, or rewire the trailer side connector. If everything does match up and you are still having a problem then there is a problem on the trailer that you will need to track down.

Start with checking the ground connections on the trailer. The main ground from the plug needs to be attached to a clean and corrosion free bare metal surface. The grounds for the trailer lights should also be attached to clean and corrosion free bare metal surfaces. They cannot be attached to areas that are painted. If you have a plastic license plate holder, that could cause a bad ground.

You will also want to check the trailer and vehicle side connectors, and the adapter if you are using one, for dirt or corrosion in and behind the connectors. If the lights worked at the shop but not with the tow vehicle you are using, it could be a corrosion issue.

expert reply by: Michael H

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