[targa80]

The three small diodes are called exciter diodes that provide the feedback signal from the alternator to the voltage regulator. The diodes will over time fail due to heat damage (they become brittle and cause an open in the signal path) each exciter diode taps off of one of the three main power rectifier diode banks. A loss of one exciter diode will cause a low voltage output from the alternator and will cause the battery to be under charged. I have had this fault twice since 1991. The first time in 1994, I had the charge light on low idle and it dimmed with increased rpm's. Replaced all three with 1N4001 general purpose diodes.(note all three diodes disintegrated while removing them). The second time in 2017, one of the 1N4001 failed and only caused the low voltage output (under 12V) the charge light did not come on at normal idle. The only way I knew I had an issue was when I could not start the car due to a dead battery. Changed the bad exciter diode and fixed the problem. Also added an old school VDO volt and ampmeter combo where the ash tray use to be just so I have a reliable charging indicator besides the idiot light.

The only way I could imagine an over charging issue is if a rectifier diode shorted instead of an open failure.