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Troubleshooting Trailer Lights Not Working


I have a bass boat that my family has owned for probably 15 years and we recently got it back out after sitting for around 10 years. Hooked the trailer up to check the lights and they all work perfectly when the headlights are off on the tow vehicle. However when the headlights are turned on all lights still work except for the right side brake/turn signal which instead just stays at full illumination at all times instead of getting brighter when braking or blinking when turning. Have no clue why this is happening as the light will illuminate but not flash or dim only with the headlights on. Any insight will help, thanks.


Expert Reply:

The first thing to do is take a look at your owner's manual to locate any trailer fuses or relays and ensure they are all there and in working order. If they are, in order to determine the specific problem you will need to purchase a circuit tester if you do not have one - the very handy Cordless Circuit Tester # PTW2979 would be my strong recommendation due to how easy it is to use - and test the connector on your vehicle after disconnecting it from your trailer. Check the wiring going into your harness from your tail lights 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. You will also want to check both your vehicle and trailer connectors for corrosion, which can be green or white in color.

A build-up of corrosion can interfere with the signals getting through the connectors so if it is present you are going to need to either replace the plug or clean the corrosion. You'll also need to make sure your grounds are attached to bare metal surfaces and free of any paint, dirt or corrosion.

Finally, check your wiring thoroughly to ensure there are none that are crimped, broken or otherwise damaged. I have added links to a pair of help articles on trailer wiring, including a troubleshooting guide which I highly recommend taking a look at.

expert reply by:
Kyle S

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