No trailer power when connected to the truck hitch. Why?

I'd check the fuse box on your TV. I had that happen to me this spring. Had to pull the TH out of the parking spot to air up the tires. Didn't bring a battery. After driving it around the lot I realized my TH battery cables were flopping around. Sure enough nothing on the TH worked. Pos must have grounded to the frame. After looking into it. I found a fuse in my TV had blown. $3-4 later, back in business.
Before I get beaten up on this post as well, I only drove it around the parking lot without a battery.