Diagnosing Failed Alternator

[MDMooney]

Hello fellow bravo owners. I’m wondering if someone would help me think through what I believe may be a failed or failing right side alternator.

During pre-flight checks I performed my run up and was extra attentive to the electrical side of things as I recently had an avionics upgrade. With both alternators in the on position I see over 28volts and no annunciations. When flicking the left side of the alternator switch off I get an appropriate left annunciation on the panel but also see a low voltage annunciation and my volts drop to around 24. Flicking the right side alternator off I see no further reduction in volts but the right annunciation illuminates. Turning on the left side of the switch with the right remaining off I see an appropriate right only annunciation on the panel but no low volt annunciation and volts again read over 28. This leads me to believe the right side alternator is not contributing, but  why then does the annunciation extinguish when the right side of the alternator switch is positioned on? 
 

Anyone who has some insight to the switch and annunciator panel wiring is greatly appreciated!

[LANCECASPER]

8 hours ago, MDMooney said:

Hello fellow bravo owners. I’m wondering if someone would help me think through what I believe may be a failed or failing right side alternator.

During pre-flight checks I performed my run up and was extra attentive to the electrical side of things as I recently had an avionics upgrade. With both alternators in the on position I see over 28volts and no annunciations. When flicking the left side of the alternator switch off I get an appropriate left annunciation on the panel but also see a low voltage annunciation and my volts drop to around 24. Flicking the right side alternator off I see no further reduction in volts but the right annunciation illuminates. Turning on the left side of the switch with the right remaining off I see an appropriate right only annunciation on the panel but no low volt annunciation and volts again read over 28. This leads me to believe the right side alternator is not contributing, but  why then does the annunciation extinguish when the right side of the alternator switch is positioned on? 
 

Anyone who has some insight to the switch and annunciator panel wiring is greatly appreciated!

Are both of them the original ES4009LS alternators?  Or has one been changed to a Plane Power alternator?

[MDMooney]

Both are the ES-4009LS 

[LANCECASPER]

Both are the ES-4009LS 

It sounds like you have one that needs to be rebuilt. In 2018 I sent both of mine to Aero Accessories in Van Nuys CA. They did a great job. 

[MDMooney]

Awesome thanks for the help!