Attach a volt meter to the battery at rest. A battery capable of starting the engine will read at LEAST 12.8V. Start the engine. The reading will drop to about 10V while the engine is cranking. Less than 9=time for a new battery. As soon as the engine starts, the voltage should increase to substantially more that it was at rest - anything from 13 to 15.5V depending on exact model and the state of the battery. If there is no increase above the at-rest value, something in the alternator/regulator system is suspect. If the engine has a separate square regulator block, as a further test disconnect the yellow wire and measure the voltage on the wire coming out of the engine (running at full speed). This should be about 26V AC. If not, the alternator stator (under the flywheel) is duff. If this checks out, but there is no (or low) charge, the regulator block is duff.
phil_saunders(a)bigfoot.com
Phil Saunders, May 2011
