Problem with trailer hook up
 

I bought a new trailer. When they delivered it the guy had a Ford Dually and said the tail lights and blinkers don't work on the trailer. We hooked it up to my son's Chevy truck and everything works fine. So I thought the guy that delivered the trailer must have a blown fuse.
Last nite I hooked the trailer up to my RV. No tail lights, blinkers or brake lights. I checked the female coming from the RV. Everything works on all the pins like it should. I have side blinkers on the trailer and they work. Everything works on the trailer except for the tail lights. Could this be a bad ground on the tail lights? Maybe a bad ground on my reciever?
Thanks for your help.

possibly a ground issue, but it could be the wire in the plug on the trailer is not on the same pin on the truck plug, there are 2 tail light pins on a 7 way plug. Thats probably why they worked on your sons truck, but not the rv. Turn on just the tail lights on your rv and check which pin is hot, then do the same on your sons truck, I bet they are in different locations. I run a jumper wire to both pins on my trailer so they will work on whatever I decide to pull with.

THOSE AGGRAVATING TRAILER LIGHTS
 

If you are getting no voltage to the bulb base then look for a bad ground or a broken wire is where I would start...Broken ground or broken hot wire could be it...Even if your running a ground wire the trailer is also getting a ground thru the hitch on the truck when hooked to it....Good luck