Last summer on the way home from Minnesota I noticed my backup alternator regulator’s warning lamp started flickering like a candle at the Haunted Mansion.  The lamp indicates that the voltage on the bus has dropped below 13 volts and triggers the backup alternator to begin providing power.  

After trouble shooting (with lots of help) I decided to:

• Ohm every wire in the charging system.  All A-OK!
• Take the primary alternator off and have it tested at an alternator shop.  It received a clean bill of health.  I reinstalled it and the issue persisted. 
• Pulled primary alternator back off and replaced the brushes and internal regulator.  The issue persisted.
• Pulled the primary alternator back off an replaced its diode pack.  The issue persisted.
• REMOVED the internally regulated Plane Power primary alternator and replaced it with a B&C LX60 alternator and external regulator.  Issue persisted.
• Sent the backup alternator external regulator in for inspection to B&C.  They said it was fine but decided to update the lamp driver and sent it back to me.  I installed it and the issue persisted.
• Installed a new backup regulator.  Issue persisted.  
• Removed the backup BC-410-H alternator and sent it in to B&C for inspection.  Their computer said it was fine.  They put it on a bench and ran it for 2 hours to get some heat into it and it tested fine.  They did say the bearings sounded noisy and recommended replacement of the bearings although the unit was performing to spec electrically.
• Installed an overhauled/swap unit BC410-H and the issue was resolved!

While B&C was never able to isolate the issue within the backup alternator and find the smoking gun, I can say that their support was top notch.  I spent many phone calls with TJ.  From a customer service perspective they went above and beyond.  After I bought the (turned out to be unnecessary) replacement primary alternator/regulator, they send everything else gratis.  This type of support and service is legendary.

Plane Power regulator and brush kit getting replaced.

Plane Power diode pack getting replaced.

Plane Power diode pack old vs new.

New B&C LX60 unit on left and old Plane Power unit on right.

B&C LX60 install bracket as provided by B&C.

New B&C LX60 installed.  The gray “arm” is from the Plane Power install and was removed after this picture.

New primary regulator installed pilot side of the firewall.

Mounting pad before cleaning and install of new backup unit.  I replaced both gaskets.

Old BC410-H (approx. 1300 hours) showing some wear and slop in the shear coupling.

New BC410-H waiting for install.