Hello,

Vacuum canisters don't make vacuum.  If your cruise is not fully functional
on your car's open throttle vacuum, your cruise control will not work in
that car unless a vacuum pump or other source of vacuum is found.

A vacuum canister stores vacuum so some accessory can work a few times
after the engine is shut down.  Power brakes would be a good example of
such a use.

If a vacuum canister is used with a cruise control, it will extend the time
that the cruise can effectively operate after a throttle open condition.
 So, if your cruise can't hold the throttle 2 seconds into a steep hill,
adding the vacuum canister might make it last ten seconds.  With Vanagons,
there are a lot of 20 second hills.

I have installed many cruise controls, and several in Vanagons.  The type
that always works for me is distinguished by a feature called an electronic
clutch switch.  In other words, it detects an engine overrun and shuts down
rather than depending on a mechanical clutch switch for that purpose.  This
type has gone through many changes over the years, and has been sold under
various brand names.  I can tell that it's the same cruise control because
some of the mechanical parts have stayed the same from one version to the
next regardless of brand.  The most recent one that I installed was branded
"AudioVox."  (On a stick shift it doesn't require a speed sensor since it
knows engine RPM.)

Mike              84 GL   58 Isetta