Oldsmobile/Buick Repair: Buick heater blower motor, buick lesabre, purple wire

Question
1992 Buick Lesabre has intermittent heater/AC blower fault. All speeds either work or don't, you never know until you turn the blower on. When the blower will not operate, there is no power going to the blower motor at the harness disconnect. I replaced heater relay (purple wire), this did not fix issue. Turning on the rear window defroster, seemed to start this problem, but it could be coincidence.

Anything else upstream of the blower motor besides the switch could be causing this? I've read about a BLOWER MOTOR CONTROL MODULE (PCM). Not sure this is upstream and could be causing the problem.  

Answer
Hi Tom,
I would lean toward the switch, although the module is definately a possibility. I have seen that in trucks, and often it can be corrected by unplugging it and then reconnecting it, which indicates dirty contacts.
But start at the switch, and see if there is power beyond it.

Van