[Mysterytrain]

Do you have 12 volts coming into the 3 speed switch? It should be on the black wire when the ignition is in the run position and the red levers are pulled up. I've re -colored that black wire in bold red so it will stand out in the drawing below. If you have 12 volts on pin 4 of the engine compartment controller then you should see 12 volts on pin 3 of the 3 speed switch connector. If you don't have 12 volts coming from the engine compartment controller then I would bet the controller is bad. I also outlined the switch in blue.




The second drawing is a flow diagram of the engine compartment controller. 12 volts is going into the controller on pins 8 and 3 [red lines in the drawing]. The voltage on pin 8 travels to the first relay [blue] where it waits to be sent to the rear blower. When the blue relay closes it sends voltage out thru pins 5 & 6 to the rear blower , it also sends voltage to the reed switch [yellow] and then to the footwell blower relay [orange]. Since you say the rear blower works..then the blue relay and all its logic circuits are fine.
I would ck the ground on pin 2...that needs to be intact to make that orange relay work. Then I would check to be sure that there was 12 volts on pin 3...if there is then I would look for it on pin 4 thats the wire connection that feeds the 3 speed switch and the blowers.


Couple of questions..is the rear blower new? is it a factory part? We got into a nice long thread about this because the rear blower has to operate in order for the footwell blower relay [orange] to turn on..that is done with the reed switch [yellow]