ok, lets start the trouble shooting.
with the van off
positive side of the battery to negative side of the battery reading=
with the key in the run position but the engine off

the ballast resistor should have 2 connectors on it.
what is the highest voltage reading you get using the battery negative and the ballast as the postive?
you can also unplug the vr and check the pin with voltage using the case as ground when it is bolted up to the body, what voltage do you get there?

if either of this is different than your first reading at the battery, you need to start checking a few more things.
does the voltage at the vr change if you use the battery ground instead of the case as ground?
if not then you have to start chasing the positive side back.
the positive passes through the bulkhead connector 3 times.
you can bypass this temporarily to see if your problem goes away by running a wire directly from the pos of the battery to the highest voltage side of the ballast resistor.
this will back feed the system with battery voltage directly so it isn't passing through the bulkhead.

start the van and check charging again with the bypass installed.
if that works, then it is a bad connection in the bulkhead that needs to be cleaned or replaced.
you will have to follow the line or check the wiring diagram to see which ones need to be checked.