Troubleshooting Issue with No Activation of Left-Side Trailer Taillights

Question:

Think the problem is on my trk. Have 2 small trailers and in both left light does not work. Is there fuses for each side of the trailer under the the trk rear bumper? Or the harness under the bumper bad?

asked by: Vicente D

Expert Reply:

I can definitely help you troubleshoot the issue.

The first thing you need to do is make sure to check your grounds. Grounds should always be mounted to a clean piece of metal on the frame that does not have any rust/corrosion.

Secondly, even though you said you already tested the connection, I recommend checking the 9 o'clock pin specifically on your truck's side. This is because the 9 o'clock pin on your vehicle's side is the pin responsible for your right turn/brake lights. If you are getting a proper signal on that pin, you can conclude that the issue is on the trailer's side. If you happen to need a tester, I recommend using the # PTW2993.

If you determine that the issue is on the trailer's side, test the connections on your trailer plug with the plug connected to the vehicle to make sure the signal is getting through. If the signal is not getting through, you know the issue with the trailer's connector.

For a signal that does get through to the trailer, the issue could lie with the wiring on the brake lights themselves. Make sure to check the wiring for any broken or frayed wiring or loose connections. It's also a good idea in order to check out the grounds of the lights to make sure they are properly grounded.

I went ahead and attached a diagram that shows the typical pin layout on a 7-way plug.

expert reply by: Bob C

Pin Layout on 7-Way Plug
(click to enlarge)

Vicente

1/1/0001

Bob C.

6/30/2022

The fuses for your vehicle-side trailer light functions are at the front of the truck in the fuse box. According to my research on your 2003 Chevy Silverado, that is fuse #14 on your instrument panel fuse box. I recommend checking this particular fuse to make sure it is not blown.