The diagrams are posted here, but I also bought a physical copy from a vendor on eBay.
FYI - When you are looking for a service manual, the 1975 manual is a supplement to the 1974 Service manual. There is no base 1975 Service manual.
The blower motor on A/C vehicles has a couple parts to the wiring. The lower speeds are controlled by the switch and the resistor pack under the hood located on the A/C plenum, but high speed works differently.
High speed for the blower is controlled by a separate blower relay, also located on the A/C plenum. Power for the high speed relay has separate 30 amp fuse in a round fuse holder that is located on the upper edge of the firewall, just under the hood. This fuse only comes into play when the HVAC is on high speed, or the A/C is on max (which kicks in the high speed). In my case this fuse holder had melted, and I had no high speed. Changing the 30 amp fuse only caused further deterioration of the holder, so I spliced in a blade fuse holder, and have had no more problems.
I also found there were variations in the blower motor and wheel assemblies, so I had to bring the old one in and match to what they had available. The way the blower wheel attaches to the motor is different for the two types of motors, and they used both motors in 1975.
Bruce
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