Hacking an RC car controller to implement a joystick (PWM)
Transistors might work if all the switches connect the inputs to common negative.







simulate this circuit &ndash; Schematic created using CircuitLab

If the switches connect one pin of the chip to another then you may have more difficulty. You'll need to trace out the PCB tracks.







simulate this circuit

Your micro will have to share the COM (-) with the RC battery negative.

It should work.