Hi!

We are trying to hook up our new 2006 F-350 to our 1998 Cherokee gooseneck. Whenever we plug the adapter into the truck the passenger side wheels on the trailer lock up. As soon as we disconnect, they are free. Help!

I think you have 2 problems.

The trailer brakes are wired together so I think the left or driver side brakes may not have been working with your old truck.

If you have an adapter between your trailer plug and truck get rid of it and put a seven way on your trailer. Those adapters go bad, don't work with all trucks and are just a pain in the butt. To easy to get lost and then you are really USC.

Your trailer should have a wiring diagram on it somewhere and the flap that covers the truck plug should have one on it.

Listen to giddyupmatt. Get rid of the adapter and install a trailer plug that matches your truck. Check the wiring from side to side on your brakes. All four should activate at the same time, it sounds as if one side's power source is open. I would check to see if your adapter is powering the brakes from your aux lighting circuit which is usually hot all the time.

Gard

"Whenever we plug the adapter into the truck  "   ???

This sounds like the brake wire is transposed in the adapter.  This is a common issue. 

http://www.horsetrailerworld.com/home/wiring.asp  These diagrams should help.  Good luck...

http://www.accessconnect.com/trailer_wiring_diagram.htm

The attached file is the pinning for C&C Trailers with electric or hydraulic brakes...