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The switch (in the control head), the Relay (below the blower motor), the resistor bank (in the evap housing). That's about it for possible Components that might be bad. There is always wiring/connector stuff that Might be the problem.
Or, of course, the blower motor Itself could have died...
BTW - the power to the Switch comes from the A/C fuse, the power that feeds the motor itself (thru the blower relay) comes directly from fusible link A.
If you don't already have it you would be well advised to get the FSM for the car. There is no substitute for that Helm manual for troubleshooting stuff like this
Just a couple of subtle differences in the schematic that Agent86 has (presumeably for an '86 model year) and My 1985 FSM..
The power to the relay is from fusible link A (not K), the color of the wire between the relay and the A/C control head (switch), at the Relay, is Orange (not Brown - Orange all the way, the color does not change at connector #162).
Otherwise the two model year's appear to be the same.