Audi 80 oil pressure warning system

[P.Dooley]

The oil pressure light and buzzer are on constantly in my 80.(when
running, any load or RPM).  
I checked the oil pressure with a mechanical gauge, it is fine.
Both of the pressure switches test good, they are open when they should
be and closed when they should be.
The Bentley manual says if all test good, then the dynamic oil pressure
control unit(DOPCU) is bad.
 
I would like to check the wiring, but don't have a diagram(my Bentley is
for VW Golf, the wire colors are different).
 
Does anybody have a wiring diagram they can send or any more information
about what would be causing the buzzer and light to stay on?
BTW, the tachometer is dead too.  The Bentley says the DOPCU gets a
signal from the coil, the tach does too.  I thought there might be
something to this.
 
Any help, thoughts or ideas appreciated.