Motorcycle Repair: Charging System, wire colors, best guess

Question
Hey Dave, I have a pagsta cruiser I've been given by one of my mates and when i picked it up it wouldn't start. Tested the battery and it as dead so i went out and bought a new one. Fired up and ran perfect, then over time it got sluggish and eventually this battery has died as well. so its like its not being charged from the stater or whatever. I've only worked on cars before with alternators so i don't really know how to go about checking how it charges. Also the wiring on it is really dodgy with wires twitched together and melted joints. So i was thinking of replacing all the wiring and joins i can see. Can you think of anything else to help me please? By the way there is this round little black plastic thing with two pins on it which goes into a plug with three holes. the wire colors are green black and grey. sometimes the bike wouldn't start with the new battery in it and i would wiggle this thing and it would complete a circuit and start running again. Any help would be much appreciated. Thanks Jay

Answer
Hi Jay,
I think the first place you should start is replacing the wiring harness. Wires twisted and melted are a sign someone didn't know what they were doing. As to the thing that has two wires and works when you shake it? My best guess there is that, that is a fuse or breaker of some kind. I have never seen this particular brand of cycle so I cant be absolutely positive. As to the description you gave me that sounds like what it could be. Now if you understand the alternator on a vehicle, cycles are basically the same concept. They should charge around 13.5 to 14.2 volts DC. Test the charging system by hooking up a volt meter that is DC to the battery leads and see what you get. The big difference with cycle charging is that the charging system is in a couple different locations on the machine as opposed to a vehicle with it all built in the alternator. To check the charging system first check the field coils in the engine. On the motor there should be wires that come directly out of the engine case. They are usually on the left side of most Asian brands cycles or scooters. Check that these wires have continuity. You may have to probe around a little to see which wires connect with each other. If you find there is no break in the coils, next follow those wires to a box or small module that is connected directly in line with battery. See that this has no burns, or melted wires in or out of it. That box should be the voltage regulator. If there are no bad spots with this, hook up the voltage meter and see to it that the system charges at a constant voltage. If it fluctuates hi and low then the regulator is probably bad. Let me know how things come out. Thanks