90Q20V rear diff. self-locking and headlight washers

["Hardwick, Robert C" <Robert.Hardwick@PSS.Boeing.com>]

Model: 1990 90 Quattro 20v
Uncommanded rear differential lock:
Every now and again, at any speed, my rear diff. locks itself.  The "ABS
OFF" and green center console diff. lock lights illuminate.  Taking
parking lot type turns exhibits enough scrubbing to confirm the lights'
veracity.  Sometimes, cycling the diff. lock button will cure it,
usually not.  Occasionally, I've noted that the lights come on after
hitting a pavement joint or other bump.  So a loose connection is likely
- but finding it in that complex system isn't easy!

I have cleaned the diff. lock computer connection under the rear seat,
using Stabilant 22, but got the uncommanded lock 2 days later.
Operating the diff. lock with the button works just by the book,
switching off at 15mph.  Any suggestions?

Non-operating headlight washers:
Since I purchased the car, used, in May, the headlight washers have not
worked.  Not a drop.  The windshield washers have very powerful jets of
water.  Bentley hardly mentions the headlight washers.  Since they
cannot be commanded separately from the windshield washers, I'd assume
that they're operated by the same pump, but there are separate
reservoirs for the windshield and headlight washers.  Access to the
hoses, etc is very difficult.  Bentley's instructions for replacing the
actual jets has you disassemble the entire bumper.

Does anyone have troubleshooting suggestions, or at least a schematic
description of operation?

thanks, Robert