Low charge to no charge issue pulling hair out

J.B. said

RUNNING battery at 12.4 not charging at 13.5-14. If I remove voltage regulator connection charge drops even more to 11.9

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It is charging but it does not need much so the alternator is putting out a maintain charge.

A battery with higher internal resistance might cause what you are seeing.

Also testing wires with an ohm meter will tell you at least one strand of wire is connected.

To determine wire health you need to check for voltage drop under load.

The smaller wire diameter (gauge) the higher resistance under load = more voltage drop.