I dont think this will work on a vanagon,but one simple way is to touch the
rear bearing cover with a screw driver when the engine is running. If the
cover is magnetic, the altenator is ok. If not , replace it. Thats all.You
see, the rotor is a rotating magnet,and the rotor shaft contacts the
bearing cover, so it becomes magnetic too.I suppose the front pully is
magnetic also, but I cannot figure out a way to test it for magnatism.