Hi Johnny,
Have you put a meter on the vehicle when the engine is running and monitored what the voltage output actually is? Let me know what it is actually doing that way we can see if we have a charging system issue or a monitoring system issue.
If the alternator is putting out less than 13.5 volts at idle, rev it up and see if the voltage goes up.
One issue that people always over look is the tension on the belt. If the belt is a little loose then the alternator will not spin fast enough causing an under voltage issue.
Then we need to inspect the cables and make sure they are clean and tight. Then make sure they are not worn so they can't carry the current.
Let me know what you find and we can go from there. Thanks
https://www.2carpros.com/articles/everything-goes-dead-when-engine-is-cranked
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Thursday, July 18th, 2019 AT 7:38 PM