I traced out a schematic for the LED display's circuit board from my
'84 camper.  Some listees have been asking about these things, so I've
posted a copy to my web site. It can be found at:
 www.ns.net/~sgreen/vw/display.html

It shows what's really inside the gray box in the Bentley wiring diagram.
Interesting stuff if you know how Op Amps work; pretty arcane otherwise.

The page also includes a plea to those who would attempt to repair
one of these things:  DON'T, unless you're sure you know where the
problem is, and you're sure you know how to fix it.

Steve Green, Folsom, CA
Zefram, 1984 Wolfsburg Westfalia