12v 7 pin power

Wait, are you saying the 12v+ at the plug is hot all the time? LOL

Seriously, the first place to start is in your owner's manual, which you can find online HERE.

Look in the fuse panel in the engine bay, should be by the battery. Pull off the plastic cover and look at the fuses. This is from page 10-34 in the owner's manual:


Location 68 (circled in red) is the fuse for 12v+ power at the 7 pin plug. If there is a fuse there pull it and see if it's blown, or if it's a dummy. In my series of Suburban they left the fuse location empty and supplied the fuse in a baggies in the glovebox along with the pigtail for the brake controller. I have heard that later models were shipped with a dummy fuse installed. So you have to actually pull the fuse and see if it's a dummy or blown.

99% that's your problem.

SoundGuy wrote:


GM hasn't changed anything ... Ozlander said "relay", not fuse. Yes, a new GM truck will often have a dummy plug in Stud #1 which one must replace with a fuse but this charge line circuit is not controlled by a relay as it is in Ford trucks.

Good advice. OP needs to confirm what is in Stud #1 is a fuse and not a dummy.

KJ

This GM vehicle will not have a relay. You do not need the lights on, engine running, in gear, etc.
When working properly you will have 12v at the 7 pin ALL THE TIME.
Did you buy this new or used? If new and YOU didn't attach the wire then it's not attached because for some stupid idiotic reason GM doesn't do it.

Also check that the RED/BLACK wire under dash for trailer harness is actually connected and not just hanging

OP:
You said a wire by battery, verify that previous owner has not added this along with an in-line fuse or a battery isolator. Trace wire in the engine compartment.

I assume there are no other connections between the fuse by the battery and the rear connector. Very odd to have a continuous wire break in the middle. If there are connections test them. Otherwise you need to follow the wire and find the break.

Mandalay Parr wrote:
Did you try it with the engine running?

Once again - GM charge line is wired to be hot all the time, regardless of whether the key is even in the ignition.

GM has been constant hot for ever.

Did you try it with the engine running?

Ozlander wrote:
Also, I think there is a relay you have to add.
I think all the info is in your owners manual.

SoundGuy wrote:
Not in a GM, the charge line is hot all the time.

donn0128 wrote:
When did they change that? If has been nearly for ever than on GM products there is a dummy fuse in the underhood fuse panel that needs to be replaced with a real fuse.

But, if the OP has power like soundguy pointed out then the OP has a trailer wiring issue he needs to trace out.

GM hasn't changed anything ... Ozlander said "relay", not fuse. Yes, a new GM truck will often have a dummy plug in Stud #1 which one must replace with a fuse but this charge line circuit is not controlled by a relay as it is in Ford trucks.