Inaccurate auxiliary gauge readings

[steveb@newkla.kla.com (Steven Buchholz)]

I reviewed the wiring diagrams for the early '80s Audi 4000 & Coupe and found them 
to be very similar to my '78 Fox.  It appears that the auxiliary gauges mounted in 
the console receive *both* power and ground from the same wires that supply the fresh 
air fan.  Upon further consideration I think I was slightly off in my theory of the 
source of the problem.  I said before that I thought it was a voltage drop in the +12 
supply that caused the problem, but the same thing will happen to the ground.  The 
sensor return comes through the ground ... any voltage drop in the ground line due 
to the current drawn by the blower motor will affect the gauge reading.  Whereas it 
might take some work to find an alternate power source, separating the ground should 
be pretty straightforward.  I did notice that there was an unused connection to the 
same fuse used by the fresh air fan on one wiring diagram I saw.  It would be possible 
to add a new wire to this terminal an eliminate the voltage drop on the +12 supply.  

Didn't find a wiring diagram showing the LED auxiliary gauge panel so I still can't 
say for sure if the panel uses straight battery voltage or requires an external reg-
ulator.  It looks like there is a terminal on the dash gauge assembly connected to 
the regulated supply that drives the fuel and water temp gauges, meaning that it 
could be possible, but I still doubt it is really used.  

Steve Buchholz
s_buchho@kla.com