Chevrolet Tahoe 2008 Owner's Manual page 54

Your vehicle is equipped with wiring provisions for a
12-volt battery power supply. Refer to the following
information when adding electrical accessories
that will use the 12-volt power supply feeds
connected to your vehicle's electrical system.
14-22
The wiring harness is located below the instrument
panel near the center of the vehicle. The following
information describes the breaker and relay location
and provides a wiring diagram to aid in connecting
customer equipment.