Why would you want to put a relay on it/make it a switched circuit? The engineers at GM are not complete knuckleheads. The ECM will not let your trailer battery drain your truck batteries beyond a certain level so that you will always have enough juice to crank it. Just plug it in and forget it.Me again. I just went and looked at the fuse block again. It all makes sense now. "Stud 1" and "Stud 2" are actually fused with fuse 61 and 62 (or something like). I checked the stud 2 voltage and it had 12v sitting on it with the truck off and did have the 40amp fuse. All I would have to do is connect the wire. Silly stud didn't have a nut though.
To make it switched instead of always on, I guess I could pick up a relay and put between the actual stud/bolt and the trailer power wire, then just wire the energizing section of the relay across ground and something switched. Just not sure what that would be at the moment. Now with these little bitty fuses, it's much harder to jumper off of one.
At least I now know how to get it working. Isn't the Internet great!