Here is a simple test to determin if your alternater is bad.    While
runing the engine , touch a screw driver to the rear altenator rotor
bering.If the berring cover plate is magnetic, your alt. is OK. If not ,
you  have a bad alt.  I am told that  the windings, shaft and berrings,
ect, all become magnetic when in proper operation.Never tried it myself on
a vanagon, but this holds true for a '8o Fairmont. I like this test-- no
expensive and hard to use gages.Nimrods like me get it right every time.