Dodge 2008 Ram 4500 - Manual (Page 368)

The Trailer Tow Package may include a 4 and 7 pin
wiring harness. Use a factory approved trailer harness
and connector.
NOTE: Do not cut or splice wiring into the vehicles
wiring harness.
The electrical connections are all complete to the vehicle
but you must mate the harness to a trailer connector.
Refer to the following illustrations.
4-Pin Connector
366 STARTING AND OPERATING