Bear with me while I attempt to explain what I'm trying to do

My goal is to be able to use both the KF-supplied pitch trim switch and buttons on the control stick.

I'm using the Ray Allen G405 stick grip. When a button is depressed, the output wire is connected to ground.

My avionics are Garmin and I'm using the GSA-28 servo. The trim switch is connected to the pitch servo which
passes the signal along to the TCW Safety Trim Booster which then controls the pitch trim actuator. The safety
trim booster is needed since we need to drive the trim actuator with more current than the stick grip can
handle.

Here's where it gets complicated. The pitch servo expect 2 signals A and B. To move the trim in one direction
you put 12v on A and Gnd on B. To move the trim in other direction you just reverse the polarity and A is Gnd
and B is 12v. This is what the KF-provided switch along with their wiring diagram provides.

The question is how do you connect the stick grip buttons and the KF-provided switch together to generate the polarity-reversing
signals? I was thinking maybe an H-Bridge might work.

Here's the wiring diagram provided by TCW:
TCW Servo Boost Wiring.jpg

Victor