your not looking at it right, the switch on the injector powersupply is to get a pulsewidth reading without turning injectors on, watch my flowbench videos and you’ll see how this works… the opti module is a grounding device–> you hook ign/inj/pwm up to where it says hook ignition coil here, then if you want 420v kickback both switches are off, if you want 68v kickback for injectors turn that switch on, if you want to run a transmission solenoid,egr valve in pwm mode turn the last switch on to make the current float, these options drive the component like it is driven in the car… first scope out how the engine controller drive signals, then use the nano to create the drive output that matched what the ecm was doing…if you dont want to use the resistor switch to set up before testing you could use an inverting schmitt trigger to invert base before the 100 ohm resistor to determine this, that would be an effective way of doing it thats not paracitic to the circuit… do you want me to draw that up?