I borrowed my brothers enclosed trailer and all the lights fine work except the interior lights.He says they worked the last time he used it. I'm going to try and check it out in the daylight so I haven't really dug into it yet.Any ideas...............

I think I would check for fuses on the trailer first. After that, would check and see if his truck has an extra wire ran into the trailer plug to power the lights.

I've seen a lot of interior lights just tapped off the running lights... so the "lights" have to be on to get the interior lights. Just take a second to check that before going exploring.

Well.......If I use the ground pin on the plug I get no voltage at all at any pin. If I ground to the hitch frame I've got voltage at all pins except the one that should be power.So I'm pretty sure that it's truck related.Thanks for the help.