I recently installed back up lights on my trailer. When I plugged the truck in to check them, they didn't work. So I put a 7-pin tester on the truck, and there's no voltage at the output. I checked it with a meter just to be sure, and there's definitely no voltage on the center pin. There is voltage at the #63 fuse when the truck is in reverse, which according to the manual is the trailer back up light fuse, but I haven't chased it down any more than that (because it's cold outside). I haven't looked at any relays, or anything else.
Any ideas? Is there a schematic of the trailer wiring that shows the wiring from the fuse box to the trailer connector? I'd really like to get this figured out at some point, especially since I went to the trouble of putting back up lights on my trailer.