It's called a "Blower Speed Control Module" - and it's hard to find nowadays.
There's an improved version that requires replacing the connector - also currently no longer available.
Looks like time to hit the boneyard to find one.
Don't toss the old one! I've got on my list of projects reverse-engineering one to make them fixable (I THINK the major problem is the pass transistor opening or shorting - but am not sure yet.)
RwP