Thanks everybody for the tips on troubleshooting.  I'm not sure of
the of logic behind a low vacuum situation causing it to
disengage.  My understanding is that it disengages for brake
application, rapid rpm change, or the whole thing being turned
off.  Also I assume it disengages when it gets weird signals from the
speed sensor.

More info:  The unit used to work very well.  It could not get the
throttle way open, especially up hill, due to drop in vacuum I
assumed.  But that was not a situation I wanted to use it
anyway.  The onset of this problem was gradual.  There was a period
where it got very erratic about when it would disengage.  During that
time I tested all kinds of situations to see what was common and
didn't come up with anything.  Hitting bumps in the road was not a
factor.  Low Vacuum situations were not a factor.   On uphills, I
could "help it" by putting my foot on the gas and when I got to the
top of the hill it would take over and stay engaged.  I tried riding
my foot lightly on the gas pedal to see if it was letting go of the
throttle or pressing it hard right before it disengaged.  It wasn't.
Sometimes it would not disengage for 30 minutes, other times a few
seconds.  Very odd.  One time a few years ago during a trip with lots
of interstate, it got to the point it was really not working much at
all.   I stopped and went through all the audiovox checks of the
wires.  They came out fine and put it all back together and then it
worked better for a while.  Yesterday when I dug into this, there
were times when the unit would not turn on at all, or at least it's
little pilot light wouldn't illuminate.  I had never seen that
symptom before.  Again, after doing the wire checks, it turned on and
stayed on fine.

Edward

At 10:03 AM 11/4/2012, Richard Koerner wrote:
>Ed, I've got the Audiovox CCS-100 on my 85 manual Vanagon.  I use an
>accumulator purchased from Napa (just good practice to have an
>abundant vacuum supply).  But sometimes the cruise control would
>disengage--I noticed it would happen after going after some bump in
>the road.  I think the root cause was that the bracket holding the
>sensor would flex and oscillate, momentarily increasing the distance
>between magnets and sensor, and the CC would lose itself.
>
>Simple solution:  STRONG magnets and a STRONG bracket.  I replaced
>the wimpy magnets in the kit with some rare-earth  (neodymium)
>magnets available at http://www.gaussboys.com/ or similar, google to
>find a source maybe a hobby shop.  And a really stiff and strong
>bracket of heavy gauge steel I had laying around (Home Depot or Ace
>Hardware) to support the sensor in close proximity to the rotating magnets.
>
>Excellent results!!!  My cruise control NEVER drops out
>anymore.  And I think having the vacuum accumulator makes for
>INSTANT response when I push the button---very solid.  A real
>pleasure to drive.  I'm really sold on that Audiovox unit.
>
>Rich
>San Diego
>
>
>
>--- On Sat, 11/3/12, Edward Maglott <emaglott3@GMAIL.COM> wrote:
>
>From: Edward Maglott <emaglott3@GMAIL.COM>
>Subject: troubleshooting Audiovox Cruise Control
>To: vanagon@GERRY.VANAGON.COM
>Date: Saturday, November 3, 2012, 7:33 PM
>
>hello, I have one of the usual aftermarket Audiovox cruise controls
>on my 86 with AT.  I think it's model CCS-100?  I use the magnet
>speed sensor kit on my drive shaft.  It's not working well.  It
>engages briefly and then immediately disengages.  It will then
>attempt to resume to that speed if I press that button, but
>immediately disengage.  That makes me think that it is at least
>remembering the speed I set it to.  I've gone through the
>troubleshooting of all the wires as the instruction manual specifies,
>and everything is good.  I'm wondering if I could devise some way to
>monitor it from the driver's seat to figure out what is going
>on.  Thanks for any advice.
>
>Edward