2024 3500 - Trailer Lights Not Working

[cstapp99]

I cross-posted this in the Silverado/Sierra forums. My new to me '24 AT4 3500 is having issues with the trailer lights on my boat trailer. The trailer lights work with the other 2 GM vehicles I have plugged into the trailer.

Additionally, my 7-pin adapter has LED lights on hit that show which circuit is being activated by the truck. None of them illuminate with my truck. They do on the wife's Tahoe.

So I took the truck to the dealer to have them diagnose the situation. They are telling me that the truck performs as designed when they hook their testing machine to the 7-pin.

When I got the truck home, I used my multi-meter to test all of the pins. With the truck running, I'm getting 14v to the 1 o'clock pin but nothing anywhere else no matter what lights I turn on with the truck.

Any thoughts on this? Can what the dealer is telling me about the test be accurate?

Thanks

 

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[F32_Sierra]

Where were you using as your ground reference?

7 o clock position should be ground and your 1 o clock is 12v constant

 

[cstapp99]

Where were you using as your ground reference?

7 o clock position should be ground and your 1 o clock is 12v constant

I was using the 7:00 pin for my ground reference.

 

[F32_Sierra]

There is a fuse under the bed of the truck. Follow the plug wires back and you’ll see a rubber fuse holder. I’d check that and check the other fuses under the hood because if I remember correctly, GM uses a fuse for each circuit for trailer plugs.

 

[cstapp99]

There is a fuse under the bed of the truck. Follow the plug wires back and you’ll see a rubber fuse holder. I’d check that and check the other fuses under the hood because if I remember correctly, GM uses a fuse for each circuit for trailer plugs.

Thanks. I will look for and check the one under the bed. I had already checked all of the fuses under the hood before taking it to the dealer. The only thing that makes me think it's not a fuse is that the dealer "test machine" said everything tested out ok.

 

[F32_Sierra]

Makes sense, but I trust the dealer only as much as they trust me.

Their “test machine” is probably one of those 7 pin trailer diagnostic plugs. You can get them from AutoZone for like $35-$40. Just search for 7 pin trailer plug tester and you’ll get some local to you I’m sure.

 

[cstapp99]

Makes sense, but I trust the dealer only as much as they trust me.

Their “test machine” is probably one of those 7 pin trailer diagnostic plugs. You can get them from AutoZone for like $35-$40. Just search for 7 pin trailer plug tester and you’ll get some local to you I’m sure.

Thanks again. I have one of those testers - built into my 7-way adapter. It's telling me no power to the trailer lights.

I just went out and tested the same pins on my Silverado 1500 work truck with my voltmeter and voila! I have voltage at the correct pins. I'm leaning toward dealership incompetence.

 

[cstapp99]

UPDATE - I remembered that I have access to a flat bed utility trailer, so I hooked up my truck up to it. Moments after plugging in, I get a flash from the truck's brake lights to indicate trailer is detected. After that, all lights work correctly.

So I'm concluding for now that this truck only sends power to the 7-pin AFTER it detects a trailer connection. That would explain why my multi-meter testing isn't showing anything. I have no clue why my 2024 1500 work truck would be different, but it is.

So now I'm back on the boat trailer trying to figure out what's going on with it.

 

[gemarsh]

That is correct, if the truck doesn't sense a draw, it won't energize the trailer light module.

I would start by looking for bad/weak ground. As all the lights don't work and it won't wake the module. I have to yearly clean the ground on my atv tiltbed trailer.

 

[cstapp99]

That is correct, if the truck doesn't sense a draw, it won't energize the trailer light module.

I would start by looking for bad/weak ground. As all the lights don't work and it won't wake the module. I have to yearly clean the ground on my atv tiltbed trailer.

View attachment 32741

Thanks! I had suspected bad grounds also. Week before last, I went through all the grounds on the trailer and added dedicated ground wires from the light fixtures all the way up to where the wiring harness white wire is grounded to the trailer frame. I can't remember if I tried my truck with the trailer after I did that because I'm constantly switching back and forth between the work truck and my personal truck. Fingers crossed....

 

[Ejays]

FWIW, I read / was told back when I had my 2015 1500 and had issues to never connect the harness with truck running. Not sure if it’s true but I follow this practice.

 

[Pingbling23]

https://www.amazon.com/gp/aw/d/B00C4AYR3U?psc=1&ref=ppx_pop_mob_b_asin_title

This fixed my issues with led trailer lights. Not enough draw so the truck didn’t think anything was plugged in.

 

[cstapp99]

https://www.amazon.com/gp/aw/d/B00C4AYR3U?psc=1&ref=ppx_pop_mob_b_asin_title

This fixed my issues with led trailer lights. Not enough draw so the truck didn’t think anything was plugged in.

Thanks! I ordered the Curt version yesterday. Hoping it fixes the issue.

 

[Pingbling23]

Thanks! I ordered the Curt version yesterday. Hoping it fixes the issue.

I’m sure it will. Boat trailer is incandescent and have no issues. Utility trailer is led and truck doesn’t like it. Last truck and my current jeep no issues. You would think things would get better with new tech lol.