Let me jump in on this thread and second the comments from Mark and others
to look for a bad connection or broken wire.  Although my experience in
troubleshooting electrical problems in Vanagons is limited, at one time in
my life I made my living keeping some large, early (pre solid state
electronics) computer systems running and learned some valuable lessons in
the process.  The bottom line is that somewhere around 80% or better of the
failures that occur in systems like the electrical or electronic systems in
the Vanagon are going to be mechanical in nature, NOT failed electronics.
So when trouble shooting pay very close attention to mechanical connections
such as grounds and connectors.  Bent pins/contacts, corrosion, and broken
wires are much more likely to be the problem than failed electronics in the
ECU or other components.
(For those interested try to find a study done in the late '50's or early
'60's by the US Navy on the negative effects of 'preventative maintenance'
in electrical and electronic systems both aboard ship and in aircraft.)