Dodge 2005 Durango - Manual (Page 277)

Heavy trailer towing also may require breakaway electric
trailer brakes, anti-sway devices or equalizing hitches for
safe operation. Such devices are commonly required by
state law.
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
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