2012 Yukon not seeing trailer connected

[gmcman]

I have the factory integrated brake controller,(JL-1) this is the 1st time it's being used as I had to connect the red wires to the studs.

Fuses are good, I have 12V at the studs.

I have 12V at the brake control relay or module located above the spare tire.

The blue wire is good between the module/relay to the 7-pin, and both sides of the 7-pin are clean.

No stored codes.

Trailer works on another vehicle, and the Yukon still doesn't work on a 2nd trailer.

I have also tried a new GM gain switch and module, still no change.

No error messages, but the Yukon still won't recognize when a trailer is connected.

Curious if anyone has dealt with this.

[gmcman]

Brakes are electric drum.

[Michelle_S]

Are the brakes on the trailer electric drum or electric over hydraulic disc??

[gmcman]

I don't know if the previous owner did, but it looked like none of the 12V leads were hooked up.

The two big fuses for the studs are in place, and I have 12V to each of the studs.

[blt2ski]

Has the Yukon pulled a trailer before? If not, my last 3-4 GMs have a big fuse that needs to be added to a fuse box in the engine compartment, drivers side.

Marty