As I reread your original post , I noticed you never mention if you even have HIGH fan.

This is important b/c if you do not , and don't also have low fan [ as your post suggest] , then the diagnosis is completely different.
If no fan speeds work , then look at that schematic and you will see a 7.5 amp fuse [ F1/1] that controls both relays primary feed side . That could cause both speeds to not work.
So , do you have high fan??????????

On to another tests , if you do have a high fan , but no low fan:
At that resistor, if you take a jumper wire and go from the battery +terminal and jumper to that resistor where the single wire terminal is [ not the 2 wire one], does the low fan run??
That will verify both Resistor and fan motor.

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A Dalton