Thanks guys.
This reading was directly in the 7 pin receptacle on the truck... with the engine running and the trailer NOT plugged in.
I don't have any idea what load would be in that circuit, and I don't think there should be, at least not on the truck.
I am thinking that it almost has to be inside the other side of the receptacle, where the truck's wiring harness plugs into the receptacle. I had to clean this out a few years ago, it probably just needs it again... at least I'm hoping so
. It could possibly also be a relay, but with no load, I would think it would/should still show system voltage, unless the resistance across the relay is EXTREMELY high.