Jeezo-Peezo Grahm ;
You're making me remember my youth in Rural New England fixing old tractors and rusted out pickup trucks in the snow....
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Anyway, if the belt(s) is/are tight enough to make a squeak sound when you force the pully to turn they're fine, don't sweat one being slightly looser, as I said before ; NOT AVAILABLE in matched sets no matter what B.S. the Dealer says .
If the battery shows 13.9 or better VDC once it's started (with everything turns off) the alternator and belts are fine .
If less voltage, first check at the back of the alternator to see what it's putting out, most non BOSCH branded regulators/brush holders don't ever charge above 13.4 VDC, why I only accept BOSCH brand regulators .
If the dash light is out and it's starting O.K. in the cold, stop before you do get frostbit ~ I remember frost bitten ears, not much fun .