If a new battery isn't holding a charge, the reg/rec COULD be at fault. To test, put multimeter leads with meter in VDC scale on the battery. Start and rev the engine to 4K rpm. Voltage SHOULD be ~14.5 VDC. If it is not, then the problem may be you are not getting enough power TO the reg/rec. Take off the blue plug on the side which is the connection from the stator to the reg/rec. Start the engine and measure the voltage using your meter (IN V/AC THIS TIME!!!) Measure between any two of the pins. The pins will be connected to all yellow wires OR to blue,red and yellow wires. In any case, you should have 50VAC between each of the three pins (measure all different ways). If you have less, then either the stator or rotor are bad. The stator is the windings inside your cover and the rotor is the big magnet on the crank end. If the stator is bad, you can tell by checking resistance between the pins on the same plug. Turn off the engine and measure with the multimeter in lowest ohms scale. All resistance measured between pins should be about .05 Ohms if you get a bunch more or less, the stator is bad. You can also measure resistance between a case ground (put your black/NEG meter lead on the engine) and each of the three pins. I believe you should see a "ONE" on the meter for each or they have open windings. Double check a manual for that one (memory). If the stator checks out, the rotor is the culprit. It can lose magnetism if it is banged around good and needs to be swapped out to get more AC up to the reg/rec if you find it bad.
