Cruise control switch logic

Wallace White wallace@stanfordalumni.org
Wed, 18 Jun 2003 13:36:55 -0700


Huw Powell wrote:
>> This leftmost switch is not connected to +12V but instead to the brake
>> light switch. Its "output" then runs through the CC's clutch and brake
>> switches in series, and then to the CC module.
>
> "Coast"
>
> Deactivates cruise control without turning it off, so the previous speed
> setting is remembered.  In other words, it acts just like the brake and
> clutch pedals.
>
> You forgot "off", all the way to the right.  To operate, move slider to
> "on"  Pressing the end switch sets a speed.  moving the slider to the
> right deactivates it so you can "coast", this is a momentary switch.
> Moving it to the left "resume"s the previously set speed.  If there is
> no previous setting, "resume" does nothing.

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... I double-checked that the tail lights are all functional, in
case the ground is going through them. So the Bentley isn't kidding
that, with the stalk switch at On, I should see <1 ohm from ground to
the CC brake switch connector? I'm seeing mega-ohms.

I just tried disassembling the cruise switch for cleaning. I don't see a
way to fully disassemble it (can't get the main white "piston" out the
end), but it was open enough for some spray cleaner. Didn't change the
measured resistance out at those test points. Hmm, maybe I don't need
this "coast" functionality that I never knew existed...

> and for some troubleshooting info, etc...
>
> http://www.humanspeakers.com/audi/cruise.htm

Thanks--I've reviewed your site too, naturally. And I did clean the
brake and clutch switches as you suggested a while back. The Bentley
warned that the switches would be destroyed by removing them; I'm glad
you knew better. They're much better now.

- Wallace
   '87 5kcstq 203k