Pardon me if I butt in here, but I can't help it. I'm looking at a way of keeping my antenna up all the time when I want to, but easily being able to get it to go up and down with the radio going on and off. (See 'Winterizing an antenna')

From the interesting posts I've read on this subject, here are what I believe are the facts:
- Most antennas have a trigger wire, a constant wire, and a ground.
- In most cases, applying 12V + to the trigger wire makes the motor turn in a direction that extends the mast.
- In most cases, applying 12V + to the constant wire makes the motor turn in a direction that retracts the mast.
- After retracting or extending the mast fully, a circuit in the antenna disconnects power to the motor.
- Some antennas use 12V - for the trigger and constant signal. Using a relay will enable you to flip this to 12V +.

So, regardless of how the source of the 12V is switched on or off (radio trigger wire, IGN or ACC switch, remote amp lead turn-on wire), any 12V signal fed to either wire will make it go up or down. If there is no signal to the trigger wire, but 12V to the constant wire, it will stay down. If there is no signal to the constant wire, but 12V to the trigger wire, it will stay up. If both 12V sources are removed, it will remain in the position last in when the sources are disconnected.

Here's a speculation:
- The switch on the older Mercedes that allows you to 'bump' the mast up or down is a combination momentary contact/on/off that inches it down with 12V pulsed to the trigger (up) wire, or the constant (down) wire.

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1986 560SL
2002 Toyota Camry
1993 Lexus