I've been thinking about installing a kill-switch as a theft-prevention
mechanism.  I know that there's a wire up front in later year vanagons that
affects the coil, which has been discussed on the list before.  Does anyone
know of any similar dash-accessible wires in an '83?
-Wes

(Here's a quote from a post from Dug Smith a few years back on the wire the
later vans have:)

Well, just for the archives, I finally wired up the immobiliser circuit
tonight.  As Matt suggested (thanks, buddy), there's a line into fuse 12
that runs the coil (circuit 15 on the wiring diagram).  I unplugged it, the
van wouldn't start.  I plugged it back in, and it started.  I unplugged it,
and the van stopped.  Excellent.  It's a black wire, on the bottom connector
to the fuse box, and having a female spade connector, went happily into the
relay I'm using.  Everything's sorted now :o)