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> << What I'm wondering is why the plunger switches
> on the clutch and brake interupt the flow of power to terminal
> 3 of the control unit. The switches don't even see power until
> the brake pedal is depressed and power is sent to the brake
> lights. So what is the point of then interupting this flow if it
> was only just initiated? >>
> Basically, the gist is that the switches find a ground path thru
> the brake lamp module (of thru the lamps themselves, if you don't 
> have a module).  The CC module is looking for a connection to
> ground, not +12V.  Pretty perverse, eh?  I'm not sure why Audi did
> it this way, instead of going directly to ground or +12V, like one
> would expect.
... well, with yesterday's purchase of an '85 4kQ I happened to bring in 
the Bentley.  I looked in a couple of situations and can see that the 
1985 4k operates as steve describes ... I am wondering if this is actually
another fail safe mechanism ... if the vacuum/electrical switches fail 
by sticking in the closed position, then the +12v supplied by the other 
brake switch for the brake lights will disable the CC.  With this system
the pedal switches are actually closed when the pedal is released, thereby 
grounding the input pin on the CC module through the resistance of the un-
energized brake light bulbs.  

... this does mean that there is now one more thing to check when your
CC stops working ... are your brake light bulbs burned out [or is there 
a break in the wiring to them]?

Steve Buchholz
San Jose, CA (USA)