One Trailer Light Not Working After Wiring Harness Install on 2016 Subaru Forester

Question:

I have a 2016 Forester, and had the recommended wiring harness installed. When I wired up the trailer, everything works fine except the left rear light nothing. The side light brown wire works, and the lights came on when I took the light and attached it to the other side could it be the yellow wire isnt working? I can find no break in any wire, and the grounds are good, if the yellow wire is bad would that account for no lights coming on, just in the one fixture?

asked by: Walt J

Expert Reply:

If the yellow wire is bad on the # 118467 it could account for no light coming on, and I do assume you are referring to the trailer light and not the light on your Forester. 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 - and test the connector on your vehicle after disconnecting it from your trailer. Check the wiring going into your harness to see if the 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 your 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.

I have added links below to a pair of help articles on trailer wiring, including a troubleshooting guide for you to take a look at.

expert reply by: Kyle S