[68c10airstream]

I've had a little exposure to multiplexing switches in the late 90's.

Example, factory cruise has remote controls on steering wheel. 12volts"+" is available at the horn circuit and uses it as a power source. As you press the various buttons for cruise functions each button has a built in resistor. Lets say that you press the cruise "on" button. The built in resistor drops the available 12volts "+" to say 9.6 volts and that circuit goes to the cruise module. All of the cruise buttons are connected to one return wire back to the module. Anotherwords, every cruise switch has it's own predetermined voltage value. This system is called resistive multiplexing. One power source, one return, and many functions. The horn circuit is also used because who presses the horn while setting their cruise!!, and if the horn doesn't work, neither does the cruise, forcing you to fix a safety related system to get an accessory to work.

I listed this info to give you a glimpse into just one of the multiplexing systems out there and a fairly simple one. Good luck.