Motorcycle Repair: Battery not holding charge, yuasa battery, regulator rectifier

Question
Hi Rich,I own a 1981 GL fully loaded Interstate beauty,a real headturner,she spends most of her time garaged and only comes out when we have good weather here in England???My problem is even though I trickle charge her she will not hold a charge and this is frustrating.A recent new Yuasa battery started the old girl but after a good long run and subsequent cooling down period,I switched her on but she wouldnt turn over,just the usual clicking ,then nothing,your help would be invaluable.
kind regards
from your cousin over the pond
John

Answer
John, take a volt ohm meter and measure the voltage on a fully charged battery with the engine running at about 3-4000 rpm.  It should read 13.5 volts or higher.  If it's doesn't, you have a high load on the system somewhere or you have a charging problem.  There are three parts to check..the stator, the field coil and the voltage regulator/rectifier.  The stator and field coil are easy to check with a VOM.  All three yellow wires coming out of the stator should have equal resistance and no continuity to ground.  I don't know what the field coil resistance should be but it will be in a shop manual if you get one.  The field coil should also not have continuity to ground once you unplug it from the wiring harness.  If those check out okay, it's probably a rectifier regulator.

Regards
Rich