I've been using a replacement voltage regulator for years now that will work for the JE8-81960-00-00 Yamaha Regulator.
HOWEVER you will need to reconfigure the terminals on the connection plug to match the ones on the original regulator.
The replacement Regulator is a Kubota RP201-53710 and is available OEM or Aftermarket.
Switching the connector terminals was relatively easy and the connector plugged right in to the tractor harness.
YAMAHA REGULATOR COLOR KUBOTA REGULATOR COLOR
RED - BATTERY RED
BROWN (LIGHT BROWN) - 12VOLT SWITCHED YELLOW
BLACK - GROUND BLACK
CHOCOLATE(BROWN) - CHARGE LAMP GREEN
WHITE/BLACK - ALTERNATOR BLUE
WHITE - ALTERNATOR BLUE