Circuit Description
WARNING: This page is about a different car, the 2007 Hummer H2. However, it is still accessible from the selected car via links, so may be relevant.
The navigation radio supplies power to the TV antenna module to permit the selection of the antenna set used. The radio tests the antenna select supply voltage circuit every 500 ms after the ignition is cycled to ON. The radio does this by monitoring the current draw on the antenna select supply voltage circuit.