I have two 455's and they both overcharge the battery. When I start either tractor, the voltage is around 14 volts and then gradually increases to around 15.5 or higher. I tried a voltage regulator off a 425 and it had the same result. Both tractors are in the -040000 serial number range and have the 20 Amp Denso alternator.
So...... I checked JD Parts and they show the AM126304 Voltage Regulator is a substitute for M97348. See DTAC Solution 46546. Does anyone have access to this DTAC Solution?
My SWAG is that the AM126304 is the solution to the problem. but I don't want to spend $70 if I am not sure.