what does the multiplexer do?
 

Is this the unit which all the info goes through?
Im trying to learn as much as possible about how to convert the cluster from rsx to another car, if anyone can help, it would be awesome. If anyone could help me find a site or where I can get the harness or multiplexer that would be great too.

multiplex is runing many signals through 2 wires i.e cabin lights, power windows ,climate control etc. to keep the harness size down as they make more things computer controled. so it makes the voltage go in groups so the control unit or device will know which signal is the one it wants.