1999 Yukon blower motor

I drive a 99 Yukon with dual air. the rear works fine, but the front
blower motor is inoperative on high. the other speeds work fine. I
replaced the blower motor relay located behind the glove box... still
no luck. before I throw any more parts at it, can anyone give me any
ideas? I don't believe its the motor itself, so I'm thinking switch or
bad ground?

I subscribe to ALL-DATA for this vehicle, and they have a component
test that I could try, but it involves installing lots of jumper wires.
I keep having visions of the wiring harness glowing red like a toaster
if I were to try it! Any help would be appreciated.

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