Chevrolet 2006 TrailBlazer EXT Owner's Manual page 358

If your vehicle is not equipped with the heavy-duty trailer
connector, you may purchase one from your dealer. The
seven-wire harness contains the following trailer circuits:
•
Yellow: Left Stop/Turn Signal
•
Dark Green: Right Stop/Turn Signal
•
Brown: Running Lamps
•
White: Ground
•
Light Green: Back-up Lamps
•
Dark Blue: Electric Brakes
•
Red: Battery Feed (The chassis wiring ring
terminal must be fastened to a stud on the
underhood electrical center before the trailer
feed will become active.)
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If you need to tow a light-duty trailer with a standard
four-way round pin connector, an adapter connector is
available from your dealer.
Your vehicle is also equipped with wiring for an electric
trailer brake controller. These wires are located
inside the vehicle on the driver's side under the
instrument panel. These wires should be connected to
an electric trailer brake controller by your dealer or
a qualified service center.