Dusty,
posibility 1) It's a long run for the wire all the way from ignition
switch to the solenoid which, when energized, upon turning the key, allows
12V to reach starter via heavy gauge, directly from battery. Over the
years the resistance in this wire will get so high that it will no longer
deliver enough juice to energize this solenoid. This is a very common
problem with these vans, along with the T2s and T1s.
posibility 2) The solenoid (small cylinder next to starter with small
spade connectors) may be bad or (more commonly) is gunked up and needs
cleaning and lubing.
Put vehicle in neutral, chock the vehicle, turn key to the run position
and go to the starter and jumper heavy gauge wire to the small wire spade
connector on the solenoid (make sure your tie is not hanging down over
rotating bits!).
If nothing happens, you have a bad starter or a bad solenoid. Dismantle
solenoid, clean it and lube with a di-electric lubricant. Reassemble and
turn key to start. If the starter engages, good, it was the solenoid. If
not, you have a bad starter.
On the other hand, if, when you jumpered heavy gauged wire to small spade
connector, the starter engaged, it is likely due to scenario #1, as
described above. You can either run a new wire from ignition switch all
the way back (PITA) or install a simple Starter Relay which is available
from just about any VW parts vendor that is worth a damn. This latter
option is the most commonly followed, though it is poo-pooed by the
purists. Good luck. Miguel in Durango, Co.