Haunted battery??

1982 KZ440 LTD (D)
I just popped in a new starter, have a battery that has been fully charged, and pushed the starter button to absolutely no result. When hooked up to a charger in jumpstart mode, it will start. Disconnect the charger while the bike is still running, and the lights dim. Here's the weird part: If you completely disconnect the negative battery terminal, it still gets power. Lights stay on, everything gets power like it should, but the negative terminal cable is a foot away from the battery. How is this possible? Would this be a symptom of a shorted cell in the battery, or is there possibly another explanation for this? Pretty much out of ideas beyond taking it to a shop, which I've never done and would rather not (taking my KZ to a shop seems blasphemous. And expensive.)

I would guess that the charging system is powering the lights etc.
Bear in mind that you have earth connections between the frame and engine and the generator is referenced to "engine earth".
I would measure voltage on the connected(engine not running,ignition on) battery,and then with the starter button pressed.
You should have approx 12.5v when the battery is doing nothing and ideally >9v pressing the starter.
I wouldn't be disconnecting the battery with the engine running for fear of damaging the charging system components....the battery acts as a capacitor in the system and disconnecting it could adversely affect your bank balance.
I suspect your battery is junk but do some testing and pinpoint the problem.
Oh and please don't take it to a shop...most of the "mechanics" don't have a clue with these machines!
If you don't have one I would suggest you get hold of a factory manual,it will enable you to maintain the machine properly.
Report back with readings and take it from there.

Thanks for the reply - just to clarify, I did not disconnect it while the engine was running, it was while trying to locate any possible bad grounded connections. I was cleaning up the connection with a wire brush, and turned the key, in order to check the connection with a test light, and all of the lights came on. The negative part of the battery was not connected at all, engine was off, and turning the key causes the headlights, running lights, etc. to turn on. This is what baffles me. It seems as though something is completing the circuit, but nothing is touching the negative terminal at all. This is why I suspected a shorted cell, but I've never had that for sure and I don't own a battery tester. The battery seems to be holding a charge pretty well, but when the starter button is pushed, it just doesn't have enough juice to turn the starter. It seems like something is drawing power, but this odd effect makes me think it's the battery itself. However, since this Yuasa battery was like $70 less than a year ago, I'd rather have more than a sneaking suspicion before I run out and spend that much again. And also, when a battery charger is connected to the terminals, the starter works great.

A real mystery! With nothing on the Negative battery terminal, you still have power to the circuits? Tried this with the battery removed from the bike & the Positive terminal connected?

Exactly. Positive terminal is connected, negative is completely free of any wires. Standing there on its own like that, the whole bike gets power. Lights come on like they're supposed to, and pushing the starter button causes the starter solenoid to click, and the starter makes that winding noise like it's trying to start but doesn't have enough juice. It's the strangest thing I've ever seen.

Try this - remove the battery and sit it next to but not touching the bike. Run a jumper from the bike's positive battery cable to the positive terminal on the battery. Then see if the lights come on when you turn the key. I'm guessing the battery case or negative terminal is somehow grounding against the battery box resulting in a competed circuit. Ed

650ed - that's a good idea. Unfortunately, I won't get a chance to try anything else until Sunday. If I figure it out I'll post here. I really don't think it's grounding to the bracket, but I'm open to any suggestion at this point. I'll probably end up buying a new battery in the end, but if it can be avoided I'll be pleased financially.