I believe it's the red/green. The red/yellow provides the power to the rheostat , the red/green delivers from it to the various components after going through the resistor, and the black is the ground.
'91 Tracker 8V, 1.6L, 5 sp, 4wd, 2dr, conv, CAMI, horribly rusty
'97 Suzuki Vitara 8v, 1.6L 5 sp, 4wd, 2dr, tintop, horribly purple
'61 NSU Quickly - 150mpg