Hi
I tried looking at the wiring diagram for you but it doesn't look at all simple. The radio in my GS300 SE 99 a mkII varies the height of the antenna depending on the station tuned to! you can watch it alter as you change channels.
The diagram shows three lines from the radio to the auto antenna control relay and motor, ANTB (1) W-R, ANTA (2) W-L and ANT (5) B-W. Its not clear which wire does what!
W = WHITE, B = BLACK, L = BLUE, R = RED
Sorry I couldn't be of more help, I suppose you could try powering the wires in turn to see what happens but there's the chance you could blow it I suppose! Do this at your own risk if no more information is forthcoming, good luck.
Gordon