Agree that the -400 series regulator upgrade is “1 wire” simple. Checked today and Cessna 337 is on the R1224 approved model list, so you could also go that direction and install them without field approval or STC as a PMA regulator.

PM sent Mshac. Thanks!

Cessna 400 Series Voltage Regulator Upgrade Kit
 

Hi,
My pressurized Skymaster (FT337GP, F-BXLQ, built in France in 1974) also suffers rear alternator "not charging" blinking lights since I own it (2022). Sometimes even "high volts" red light, and even total panel black out when retracting and extending gear !!
I would like to buy your kit and the corresponding installation instructions.
Is it possible, as I live in France ?
My email adress is : michel.heintz@ue-zenith.eu and phone number is +33 6 70 13 59 72.
Thank you for your answer !