Check your alt ground wire. The ground wire is the short wire from alt body connected to engine. While engine is running alt voltage is rarely 14+ volts unless you've modified the alt to charge more by installing an adjustable voltage regulator. If your alt is stock standard then it should read between 13.4 to 13.6 volts if the batt's fully charged and lower if the batt is being charged. Possible reasons for that 14+ volt in a stock setup could be failing ground wire and/or poor batt connection.

An intact looking ground wire may be failing inside or it may be just loose/corroded connectors. Continuity testing with voltmeter may or may not reveal the gremlin as voltmeter only uses small current for testing whereas ground wire deals with big currents.

Is your ground wire runs warmer than usual while engine is running? Could be hard to tell if engine parts already warmed up. Check this during first start-up of the day. This just for general checking.

A quick test would be to use jumper cable (the ones used for jumping cars). Jump one between alt body to engine and your alt voltages should read within specs. If that happens, repair/replace the ground wire.

Regards,
Amarin.