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Troubleshooting Trailer Back-Up Lights not Working

Question:

2012 Expedition Back Up Trailer lights not working. When I put the truck in reverse it is not sending the signal to the trailer so the lights dont come on and the trailer brake engages. How can I correct this? Is there a fuse or relay that I should check?

1

Helpful Expert Reply:

It could be a fuse that is causing this issue, and that's actually the first thing I recommend checking; you will need to 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.

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.

helpful expert reply by:
1
Kyle S

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