Does anyone have insight into what is the root cause (and repair) of the
FSU failure that plagues almost every 1997 to 2003 BMW?
http://www.bimmerfest.com/forums/att...0&d=1194115994

Also, does anyone have an idea HOW TO TEST a "repaired" FSU?

The "blower motor resistor", which also goes by FSR (Final Stage Resistor)
or by FSU (Final Stage Unit), is known to fry itself in almost every single
E46 (3-series), E39 (5-series), and E38 (7-series) BMW.
http://www.bimmerfest.com/forums/sho...d.php?t=143393

The problem with replacing this ~$100 part is that the new replacement FSU
fries itself just as often as the old one did, so you end up repeatedly
replacing your fried FSU every few years or so.
http://www.bimmerfest.com/forums/sho...d.php?t=528566

That's fine for most people (although the DIY is a PITA) - but I ask
this newsgroup whether anyone has any insight into WHAT is actually
breaking - and - why?
http://www.bimmerfest.com/forums/sho...d.php?t=309399

Here is the best (admittedly sketchy) wiring diagram we have so far:
http://www1.picturepush.com/photo/a/...g/12467819.png