By old VW i'm gonna guess you mean a bug, Its been years but I think the vans might have been the same.
Does it have 3 electrical connections on it or 2?
If it has 2 you just splice the wire and run it from the power source to one side, and from the other side to the light.
3 you do the same thing but use the outside 2 and leave the center one alone.
It doesn't matter which wire gets hooked to which side. If it has any more than 3 connections I'll have to try to figure out what old vw its from so I can look at my book.