​RE: Headlight Switch
Ken, not trying to challenge a guy who stocks and sells this kind of stuff
for a living, but are you sure that it's both '90 and '91 and not just '91
that has the extra pins?
Second, when the headlight switch on my '90 went out a few years ago I
replaced it with an older switch out of the used parts bin at my local VW
shop and it's been working fine for many years now (relays added).
And third, do you know the part numbers for the different switches?  At
that time we looked at the part number on several headlight switches and
found several letter suffixes on different switches.  Two different
switches with different numbers (and IIRC different pins) seemed to work
just fine in my '90.  I put in one with the same suffix that had been in
the one that went bad.​