I've got an 05 1500 4X4 with tow package.
Boat trailer with 4 pin connected to the round connector works fine but, get nothing when plugged into the 4 pin under the bumper.
Strange thing is, I have a brake light/hitch cover that works in the 4 pin.
Any ideas on why it would work with the hitch cover and not the trailer?
How much wire is there on the 4 pin before it splices into the main harness?
Thanks!

 

Mine did not work either. I didn't trace the connector wiring to the source because I didn't want to unwrap the insulation. I just gave up and spliced new connections. Make sure you get one of those 12v testers with the light in the handle, makes the job much easier.

 

That's kind of what I thought. It's really not that big of a deal.

 

Probably a bad ground somewhere, the hitch cover probably grounds itself when you put it into the receiver so it lights up.

 

That was my first thought but, the hitch cover is plastic.

 

Well there goes that theory lol

 

My 07' is the same way. I just bought an adapter for the round connector and tucked the 4 pin one up in the bumper.

 

The hitch on some trailers are used as a ground. check to make sure your trailer has good connection with the ball..

 

Well if it works with the 7 pin adapter he's getting ground via the harness and it's working, so its not grounding through the hitch. And the hitch cover working on the 4pin truckside shows he has power and ground to the 4 pin. Unless its a funky wire that supplies sufficient ground for the small light in the hitch cover and insufficient for trailer lighting loads.