Did you checked the 30A strip fuse ? It is located in the engine compartment out side of the fuse box.
I had the similar issue, I did not measure teh voltage so can not help there, but my fan did not work and strip fuse was blown. It will not hurt to try, might save you a lot of money. And if it turns out to be the blower fan regulator a cheeper option is to buty a used one from online source or a from a junk yard.
Keep us posted.

Thanks

__________________
87 420 SEL
Looking for a nice mid 80's MB diesel.
87 BMW 528e (Sold)
99 TOYOTA 4Runner
1989 Honda Accord (Sold)
1988 Honda Accord (Total)