There is a blower circuit schematic at download/file.php?id=2847
The blower speed selector switch has two parts. In the diagram, the left half is basically on/off. When in anything other than off, it takes a ground and connects it to the right half of the switch and also to one end of the heater relay, which (when ignition is on) closes the heater relay and connects +12V from the heater fuse to one side of the blower motor.
The right side of the switch is the fan speed selector part. It takes the ground from the left side of the switch, and sends it to different stages in the blower resistor. At low speed, the left side having turned on the heater relay, the current flows through the blower motor and all of the blower resistor. At the two middle settings, it routes through current through less of the resistor, allowing m ore current to flow and the fan turns at higher speeds. At the highest setting, it switches ground directly to the blower motor, bypassing the resistor, allowing the fan to turn at full speed. Even with the blower resistor not installed, the fan should still work at the highest speed setting (normally)
Having the fan come on when you grounded the blower flange indicates several things. Since it was getting 12V, the heater relay was energized, and the heater fuse was good. It also means that the left side of the speed selector switch was correctly passing ground to the heater relay. That leaves a couple of options that could cause the symptoms.
- The switch might be bad. The connection between the two parts of the switch is internal, maybe that link between the two sides is broken somehow and the ground from the left side isn't making it to the right side outputs.
- There could be a disconnect between the ground side of the blower motor and the point where it connects to the speed switch and the blower resistor. This could be in a wire, or at whatever junction point the diagram labels as S223.
I'd probably take an ohmmeter, and with the ignition off, switch between off and the various speed settings and see if you get a ground show up at either the lower motor, the the blower resistor, or the outputs of the speed selector switch. In testing the switch, you'd need to test between the ground input and output since taking the connector off wouldn't let you test to an absolute ground
Keep in mind that the blower resistor resistor is a small number of Ohms, if the resistor is in place , you may see a few ohms at times instead of absolute dead short, depending on the meter, just checking for continuity might give misleading results, so perhaps best to do it with the resistor removed.
You said you removed the blower and jump started it. If you did that by connecting up the ground to the blower flange, then you'd want to try that again connecting the ground to the electrical connector, to test for a maybe the motor is connected to the flange but not the connector, but if you did the jump start using only the electrical connector, then nevermind.
usually blower problems are the blower motor or the resistor, yours doesn't seem to match either of those, sorry if the wall of text above is stuff you already knew