Troubleshooting New 4-Way Not Working on Trailer  

Expert Reply:

If you installed a new 4-way and you have no lights working a bad ground is certainly a possibility but there are some troubleshooting issues you can do to try and resolve the issue, starting with simply checking the fuses on your tow vehicle to make sure they are all working and accounted for. If they are, in order to determine the specific problem you will need to use a circuit tester like the handy Cordless Circuit Tester # PTW2979 to 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 will need to either replace the plug or clean the corrosion.

Like you mentioned, an important issue you will want to take a look at are the ground connections, as they can be the cause of numerous lighting problems. You'll want to make sure your grounds are securely attached to bare metal surfaces free of any paint, dirt or corrosion of any kind. Also 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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