Trailer Running lights not working

I have an 06 tundra and the running lights on my trailer don't work. They work on my buddies truck when he tows it. The fuse isn't blown and this has been a problem for years. Any advice?

 

Yes, get a test light or a volt meter out. The connection is the first place I'd check..... specially if you already checked fuses

 

First thing to check is the ground.....typically I will sand the paint off the frame and clean up the terminated connection and try again before I do anything else.
After that you can start chasing the issues with a voltmeter.....did you happen to replace any of the lights with led’s lately? Those have been notorious for causing these types of issues actually.

 

X2

 

Is your truck a Double Cab or Access/Regular? Wiring diagrams are different for each.

 

Access cab. How do I know if the relay is good?

 

And I did replace the lights with LEDs but had this problem before.

 

Check the wiring plug on the truck- there may be some gunk, grime, corrosion up in there on one of the pins. That has always been the issue for me if I had one part of the lights not work, when other trailer lights (like the brakes) did work.

 

Thanks I'm going to do that right away.

 

Here's the AC wiring diagram. Hopefully you'll get it sorted.

 

Thanks so much. I greatly appreciate that.

 

It works great on my buddies truck. So sounds like a ground to me.

 

2018 Tundra Crew Max and had this same issue 2 weeks ago towing our boat home from a trip. No running light but signals and brakes worked fine. Issue was a blown 30A fuse on the Tow Tail circuit which was not obvious to find on the circuit map as the Tow fuses are a bit spread out in the fuse block. I believe the reason the fuse blew was some corrosion I found in the wiring harness extension that is tucked into the tongue of the trailer. The brown wire and the ground plug both show some corrosion that needs cleaning up and then I think we should be good which was increasing the resistance on that wire. Still need to test but feeling confident since I found a blown 30A fuse.