Jeep 2005 Grand Cherokee - Manual (Page 286)

Trailer Tow Wiring
The Trailer Tow Package includes a 4 and 7 pin wiring
harness located at the rear underbody of the vehicle.
NOTE: Connect trailer lighting and brakes using factory
harnesses only. Do not cut or splice wiring to the brake
circuits.
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
286 STARTING AND OPERATING