Harada radio aerial

I'm sure this is probably bone simple to you guys, but to me, being electrically naive...I need help..

What I have is an automatic radio aerial (aftermarket Harada), it is currently wired to the radio.  When you turn on the radio the aerial fully extends.  It is wired like this:

Black wire to ground - Red wire to hot terminal when ignition is on - Green wire to radio which is positive when the radio is turned on.

What I want to do is install some type of toggle switch (momentary or?) that will allow me to disconnect the aerial from the radio and make the aerial operate from the toggle switch.  The purpose of all this is to allow me to choose the height that the aerial extends by making momentary contact with the toggle and stop the aerial at whatever height I choose and also to retract the aerial.  Can this be done and how would I wire whatever type switch is required?