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Strange charging issue

I have a 79 c10? Strange issue with my alternator. I swapped out my heater core yesterday and it stopped charging while running. Measured voltage off the single post on alternator and it measured 11.7v. Took it in and they said it measured good. Putting out over 14 volts. Could i have popped a fuse by snagging a wire under the dash?
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Re: Strange charging issue

Did you test it when it was running to get that 11.7v . Or did you test the batt.( running not running) To see what volts you got for both. check your fuses step 1 and your ground @ the fan motor and or firewall. One screw should make a connection to the fan body( no paint under the head of the screw then that screw should transfer to the firewall body, if has the one brass spade ground. The other spade with the rubber would be +.
If your connections are good. And your batt still under 12.5 it maybe not holding a charge.