How to Troubleshoot no Running Lights on Trailer
Trailer. I have turning and hazard lights but no working running lights
asked by: D M
Helpful Expert Reply:
In order to troubleshoot what the issue is with your running lights there are a number of steps you will need to take, which I'll outline for you. 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.
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.
- Q&A: Testing for Proper Voltage on the Brake Output Circuit
- Article: Trailer Wiring Diagrams
- Article: Wiring Trailer Lights with a 7-Way Plug (It's Easier Than You Think)
- Q&A: Trailer Brakes Lock Up When Connected to Truck
- Article: Testing Trailer Brake Magnets for Proper Function
- Q&A: Trailer Lights Work But Brakes are Not Working
- Q&A: How Long Does It Take to Install B&W Turnoverball Underbed Gooseneck Trailer Hitch BWGNRK1020
- Article: Brake Controller 7- and 4-Way Installation Kit (ETBC7)
- Article: Troubleshooting Brake Controller Installations
- Q&A: How Much Voltage Should Be Applied To Brakes on Trailer w/ Electric Brake Controller
- Q&A: Troubleshooting Voltage Drop to Trailer Brake Assemblies
- Q&A: How to Test Brake Controller without Trailer Connected
- Article: Wiring Trailer Lights with a 4-Way Plug (It's Easier Than You Think)
- Article: How to Install a Brake Controller on Chevrolet / GMC 1999-2006 Pickups