I listen to NPR in 47 flavors and like 'em all. I particularly like BBC Worldnews -- it's a touch of truth less contaminated by US political and business interests. No "sound bites" for them!

Your antenna is supplied by two key wires. The first is a "12-volts-always" source that powers the antenna motor. The second is 12-volt "signal" wire that tells the antenna control relay that the radio is either on or off. When this wire goes positive, the relay closes, and the "12-volts-always" power is switched by the relay to raise the antenna.

This "signal" wire originates with the stereo receiver.

When the 12-volt "signal" disappears, as when the radio is switched off or the ignition turned off, the relay closes and powers the antenna down.

That circuit box (the antenna relay circuit) includes a time delay so that the antenna does not jog needlessly up 'n down as you turn the key to crank the motor.
--
Don Foster (near Cape Cod, MA)