1997 GMC Savana Van Owner's Manual - Page 123

Center High-Mounted Stoplamp If items are loaded on the roof of the vehicle, as in a luggage carrier, care should be taken not block or to damage the center high-mounted stoplamp unit. If you tow a trailer that is equipped with provisions for a center high-mounted stoplamp, see your GM dealer for instructions on how to make it operate with your vehicle's electrical system. As with any electrical system by modification, have the work performed a qualified electrical service person. Your vehicle's center high-mounted stoplamp is located above the rear doors at the center of the vehicle. 2-61