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Re: 03 C4500 speedometer shows 80 when only going 35
Posted to HD/Fleet Forum on 4/2/2014

Check the alternator. Had one some time back that acted the same way. When I flipped the hood there was a brand new alternator. Unplugged and drove it ...problem gone. Scoped the alternator and saw an A/C wave where it didn't belong. Tow company that owned pai... Login to read more.