I have the exact same problem with my car. Where do you get the Multiplex control unit and is it something a novice can replace?

 

You can get one from a parts car or the dealership. Maybe even eBay has some. (didn't look at eBay)

The FAQs has a list of online parts sources.

It isn't terribly difficult work, but you might want to have someone else do it if you're uncomfortable doing it yourself.

 

what is the multiplex unit? are you referring to the body control module (aka fuse panel w/ a bunch of circuitry?)

pretty sure the brand new oem price will be pretty expensive. a wrecker might ask for a lot too but they might sell it for dirt cheap because there's pretty low demand for these parts?

 

Pretty easy to change, wire harnesses will only fit in the one plug cavity, other than some m6 bolts holding it in, although it is a pain with the steering wheel, dash panel, and seat in the way. Be sure to disconnect the battery first.