Trailer WIring Issue

SuperSilverado · April 11, 2021

Hoping you all can help with a trailer wiring issue. I have a 2020 Silverado RST, and the lights are acting weird on my aluminum boat trailer. With the truck in park and the lights connected, if I use either blinker, both blinkers operate as if I'd turned on the hazards. However, if I put the truck in gear, the blinkers work properly on the truck, but the trailer lights are very dim, or won't work at all. I have the connector grounded to the trailer frame, and both lights grounded at the back of the trailer. I've connected them every way I know how, and could use some advice. All suggestions are very welcome.

calgator73 · April 11, 2021

With the truck in drive (engine off) and in park check voltage at the connector using the ground in the connector.

Sounds like a ground issue on your trailer but this will rule out the truck.

Anacortes Army Guy · April 11, 2021

Are you using the OEM flat four connector on your truck? If so, than the issue is probably with the trailer and not the truck. If possible I'd recommend finding a neighbor or friend with a trailer and seeing if the problem is duplicated on their trailer. As you are probably well aware, assuming it's not an issue with the tow vehicle, wiring issues on a trailer are more often than not a grounding issue somewhere on the trailer.

rusty503 · April 11, 2021

Do not use the frame as a gound point. Run the ground wire from each light to the ground wire up front. Logically using the frame should work but I have seen posts on here and other forums many times about this sort of thing and running the separate wire fixed the issue.

Rob Mugs · April 11, 2021

2 hours ago, AnacortesArmyGuy said:

If possible I'd recommend finding a neighbor or friend with a trailer and seeing if the problem is duplicated on their trailer. As you are probably well aware, assuming it's not an issue with the tow vehicle, wiring issues on a trailer are more often than not a grounding issue somewhere on the trailer.

This is what I had to do to narrow down the issue for myself (albeit it was my 8 pin). It turned out to be an adaptor I had in place which I incorrectly assumed shouldn't make a difference since it was doing nothing more than adding another 4 pin connection for my light bar.

These trucks can be a bit finicky

SuperSilverado · April 12, 2021

Thank you all for the feedback. I have a small utility trailer, and the lights work perfectly when hooked to the truck so I feel sure the truck is good to go. I will try running the grounds from the lights to the main ground at the front of the trailer and see if that works. Really appreciate all your advice.

SuperSilverado · April 15, 2021

On 4/10/2021 at 10:39 PM, rusty503 said:

Do not use the frame as a gound point. Run the ground wire from each light to the ground wire up front. Logically using the frame should work but I have seen posts on here and other forums many times about this sort of thing and running the separate wire fixed the issue.

Providing a quick update on the wiring issue. Rusty's suggestion above was spot-on, and the lights are installed and working perfectly. I ran the ground wire from both lights all the way back to the front of the trailer and mounted them with the tongue ground. Thanks again for the suggestions, they were all greatly appreciated.

Rob Mugs · April 15, 2021

1 hour ago, SuperSilverado said:

Providing a quick update on the wiring issue. Rusty's suggestion above was spot-on, and the lights are installed and working perfectly. I ran the ground wire from both lights all the way back to the front of the trailer and mounted them with the tongue ground. Thanks again for the suggestions, they were all greatly appreciated.

Great to hear! I'm sure this post will be searched and help someone else in the future.

drucker · April 15, 2021

I had the same problem with my aluminum boat trailer. I tried everything but nothing worked all the time. I ran a ground wire down each side of the trailer from the plug (white wire) to each tail light. I removed all ground wires that were screwed or bolted to the trailer.

I have a flat bed metal framed trailer and a galvanized boat trailer and I didn't have to run a ground wire to each light.

All trailers have LED lights but the aluminum had to be wired different.