Rear Differential Lock

[greg erdmann <erdy@together.net>]

I've got a '95 90 Quattro Sport (love it!) and while the DIFF light on
the console (by the parking brake) lights up, it doesn't on the dash
board anymore. I got stuck in the Vermont snow the other night and
thought that engaging this would get the two rear wheels spinning get
get my sorry butt out of the snow. It didn't - one rear was spinning
while the other wasn't. 

This means it's not working, right? If not, could it be a quick
electical fix (I checked the fuse but how about a relay?) Or is this a
major "mechanical" malfuntion? Any thoughts would be appreciated folks
- I am convinced I must be missing something...

Greg