I hope this helps someone in the future.

My cruise control stopped working.  I ran through all the steps in the
Bentley and everything checked out.  I even sent the cruise control module
out to have it checked out to confirm proper operation.  It checked out
fine.  I studied the wiring diagram, tracked the current flows, etc.
Nothing, except somewhere I was losing 2-3 volts at the vacuum brake switch.
This just isn't making sense.  Then I asked my brother to look over the
wiring and he happened to mention LED brake light bulbs.  I replaced the
LED's with the original 30 year old incandescent bulbs that I had kept and
bingo, it works perfect again.  Just to confirm it, I put the LED's back in
and nothing.  Incandescent bulbs back in and perfect working cruise control
again.

I don't understand, but that was the issue.

Bob Clemmer

Perkasie, PA