[djletin]

Following advice posted around internet:

1. Checked relevant fuses - all appear intact
2. Removed blower motor transistor - checked with volt meter and confirmed between 1400-1500 ohms (1490) resistance across leads three and four.
3. Confirmed getting ~ 10.5 volts (is this low? Shouldn't it be getting closer to 12 V) from wires leading into transistor.
4. Removed "non-functioning" blower motor. Wired directly to external battery jumper pack- motor works.
5. does not work when connected to car's electrical system.

Is it transistor, blower motor, or something else?

[CaptainRich]

Voltage from the relay to the transistor should be battery voltage so that is a bit low.
Check your ground circuit. If that isn't clean and tight, the rest of the circuit won't work.

[TxGreaseMonkey]

. Check all under dash and under hood fuses with a test light or multimeter. Be very thorough. Visual inspection is often not good enough.

. Check the blower motor relay--sometimes, you can swap one relay for another in the under hood fuse/relay box (check for identical part no.).

. Check whether the blower motor will work on High. If it does, the problem is usually with the resistor.