Re: CRUISE CONTROL

["Peter Orban" <peter@amtsg6.ime.nrc.ca>]

> Date: Thu, 3 Apr 1997 8:55:14 -0500
> From: afinney@tamsconsultants.com
> Subject: CRUISE CONTROL
>
> Nobody could answer my question about the cruise control
> clutch and brake switches on the earlier 4000 series, so here
> goes again. 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.
...

Those two switches are in series and provide ground to the input of the
controller. When you apply the brake or clutch, the ground is interrupted.
There is a pull-up resistor in the controller to give the high signal.
Connecting it to the brake lights does not change this: it gets ground through
the brake light bulbs when the brakes are not applied. Why is it this way? It
could be a safety feature, if your plunger on the brake is faulty, you still
get high signal from the lit up brake lights. My other guess is that Audi could
engineer out a couple of inches wire this way, the brake switch is next to the
switch for the cruise control.  On same vintage VWs, which use the same system,
the other end of the those series connected switches simply goes to the ground.

Hope it helps, Peter

-- 
--
Peter E. Orban
National Research Council of Canada
e-mail: peter.orban@nrc.ca