"Not necessarily optocouplers, I might use a HCT14 and dual diode protect the inputs."
How about using a pic microcontroller?, it has built in dual diode protection and can sink up to 25mA current per port pin.
I will add a sereis resistor and a small capacitor to each input, would this get red of the HCT14 and the diodes?
" Optpcouplers will be overkill, you can probably handle ground noise if you route both wires fron your controller to the switches and do not rely on chassis ground. BUT as seen above you will need EMF protection."
I always use a ground wire to microcontroller board and never rely on chassis ground, but every 2 or 3 switches share one ground wires because I don't have enough wires in the cars loom, is this enough?
Mahmood