2000 ram 1500 5.2L V8. I bought the truck with a 7 pin wiring plug already installed on the back of the truck. Plugged trailer in and no lights work at all. Pulled the back off the female end on the truck to check wiring and the 7 pin is only wired for a 4 pin connection (tested and there is still power getting back there). I replaced the 40amp trailer fuse (was previously missing), but I am missing the trailer relay in the main fuse box. Doesnt even look like there are prongs inside the fuse box to put a new relay in, could this be the cause of my issues? (I know that not everything will work with only the 4 wires worked into the plug)

 

My 2001 without factory trailer tow was missing the wiring from the cab back to the rear so I wouldn't be surprised if the trailer tow relay isn't wired up either. The relay switches on power to the trailer marker and tail lights. In most cases people just connect the trailer light and brake light connections directly to the tail light wiring. The downside is that a short in the trailer wiring takes out the truck tail lights as well.