I have a 1995 Mustang with an automatic transmission. I would like to build a circuit to be able to control it with a 3 position momentary switch that I can use to cycle through the forward gears silimar to the way a tiptronic system works in BMWs or Mercedes Benzes.

FWIW, this transmission has 2 solenoids, SS1 and SS2, that control the forward gears. There is also a Torque convertor (TC) solenoid to control whether the TC is locked or not.

How would I build a circuit that can change state based on input from a momentary rocker switch?

 

or if using a 5-position rotary switch would be easier, that would be fine with me too