Trailer Light Control

Hardhands85 · March 16

I drive a 2021 Chevy 2500hd. Having an issue with trailer lights staying on. Is there a trailer light control module on my truck? The dealership is telling me no. But everything else I see online it says there is one. Does anyone know which module controls the trailer lights on this truck? Vin 1GB1YLE73MF171983

davester · March 16

What do you mean by "staying on"? They are fully on, after turning off the truck and the trucks lights are off? All the time, even the truck is running and the truck's lights are off? Or something else?

Edited March 17 by davester

chris21 · March 17

Check the ground on the trailer

Hardhands85 · March 17

11 hours ago, chris21 said:

Check the ground on the trailer

Ground is good. It does it on ever trailer I hook to. With the truck shut off the passenger side running lights and tail lights stay on no matter if the truck running or not. Getting 12v at truck plug 100% of the time .

newdude · March 17

17 hours ago, Hardhands85 said:

I drive a 2021 Chevy 2500hd. Having an issue with trailer lights staying on. Is there a trailer light control module on my truck? The dealership is telling me no. But everything else I see online it says there is one. Does anyone know which module controls the trailer lights on this truck? Vin 1GB1YLE73MF171983

You do NOT because you have the WT trim and ZW9 box delete.

All trailer lighting is handled via the relays and fuses in the under hood fuse box. Fuses 41, 55, 63, 73 and 81.

Do you have any sort of aftermarket box, dump, body of some sort installed on this?

Edited March 17 by newdude

asilverblazer · March 17

4 hours ago, Hardhands85 said:

...the passenger side running lights and tail lights stay on no matter if the truck running or not. Getting 12v at truck plug 100% of the time.

There is not a specific running/tail light for the passenger side.

The only light specific to a side is turn signal (technically this includes brake lights too).

When you say that you are getting 12v at the truck plug 100% of the time, I'm assuming that you are probing the pin labeled "Right Turn".

The only circuit that carries 12v to the trailer is the auxiliary power circuit used to charge trailer 'house' batteries or break away back-up batteries. It sounds like this circuit is somehow powering the right turn pin - whether by intention (maybe a previous owner changed the truck for some reason?) or by mistake.

Long story truck I would first confirm that all circuits going to the trailer plug are in the correct spot. gmupfitter.org will have wiring diagram and colors for the truck you can use to confirm.

chris21 · March 19

On 3/17/2026 at 7:37 AM, Hardhands85 said:

Ground is good. It does it on ever trailer I hook to. With the truck shut off the passenger side running lights and tail lights stay on no matter if the truck running or not. Getting 12v at truck plug 100% of the time .

Sounds like connector on the truck is not wired correctly

Edited March 19 by chris21