2500HD '04' 115K MILES 6.0L V8 (CLIMATE CONTROL)

2012 GMC C2500

I lost fan speeds 1 thru 3 on my climate control. I took the climate control unit out of the dash, disconnected the cable behind the dial and put a volt meter across each speed contact. There was power. I just recently lost setting 4 so I'm down to 5 which I never used before. I'm stumped here and don't know where to look next.
October 4, 2007.

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