Cruise control switch logic

[Huw Powell]

> Thanks, Huw. I see! Guess I should've read the owner's manual about
> coast... I didn't forget "off," BTW, but was just describing the
> functionality of the four electrical switches on that slider. Now I
> understand why that fourth switch exists.
>
> I still don't get why this circuit is in series with the brake light
> switch...

As far as I can tell, that is one more element in the multiply-redudant
system to turn off the cruise control.  Much as the vacuum breaking and
electrical circuit interrupting switches on the pedals act to turn it
off if you tap pedal, the brake light switch is yet another way to
instantly kill it given any evidence of a desire to slow down.

Whoops, I had another theory, too... that the cruise won't work if your
brake light(s) are out.  Now, did I ever decide which one it was...?

PS!  I reveiwed the Bentley procedure in my Coupe manual, for measuring
various reistances and voltages from place to place to troubleshoot the
system, and there was at least one error.

While I commend trying to follow the proper procedure to track down
problems, in this relatively simle system, it also helps to understand
why a given resistance or voltage should be present at any given time or
place.

It's not too hard to unplug the control module and make measurements,
and inject voltages here and there to test the circuits, once you figure
out what those R's and V's actually do.

--
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/