To test the EA1235 alternator found in many Yanmars, including 195, 240, 330, 336
1600, 1700, 1900, 2000, 2200, 2210, 2500, 2610, 2700, 3000, 3110, 3810, 4300: 

*Quick note: Yanmar also uses some Dynamo style alternators on many of their tractor models. These are small (roughly 4" in diameter) and have only 2 wires coming out of them. These can not, obviously, be tested like below so you will need to use this testing procedure for dynamos. The test below is only for the alternator style used in the models listed above. 

• Stop engine
• Disconnect ground wire from battery post
• Disconnect connectors from "Neutral" and "Field" terminals and make sure they do not contact anything or contact themselves.
• Using a volt meter set in the DC voltage position- attach the RED lead of your meter to the "Battery +" terminal of the alternator and the BLACK lead of your meter to a well grounded spot on the engine. Attaching the BLACK lead of you volt meter directly to the metal frame of the alternator is best.
• Hook back up battery ground wire 
• You should show roughly 12 volts on your meter. This is your base voltage. 
• Attach a jumper wire from the "Battery +" terminal to the "Field" terminal, making sure it does not touch alternator case or any metal. It is best to make a jumper wire with a female blade connector crimped onto one end since that plug area is a tight fit.
• Start engine and touch other end of jumper wire to the "Battery +" terminal, and observe the voltage displayed in your meter.
• Be careful not to let the Battery + wire touch metal. 

lf voltage rises to around 13 to 15 volts then the alternator is good. If you have charging problems then it is likely that your regulator is bad. Buy a new one here.  

lf voltage stays the same as the base voltage then alternator defective or you have made a mistake in your testing. Buy A New Alternator Here