What would cause an intermittent blower fan?

[jbach36]

1991 300d, 260k

The blower fan was intermittent on my car. Sometimes it would work, sometimes it wouldn't. I think the control panel inside the car is fine (maybe not, but I don't think that's the problem).

Thinking it could be the brushes on my blower fan, and with no brushes around, I bought a new blower fan and put it in. I tested it before reassembling the car, it worked like a champ, so I reassembled everything.

I took the car for a drive and.....no fan.

Could a regulator be intermittent?