Quote:
Originally Posted by FastDoc
I'd imagine it's the voltage regulator. I don't see what else it could be.
Start it up. If you rev it and voltage goes over 13.8 that's probably it.
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Electrical issues are such fun to track down. A lot easier to trace with a DVOM, though.
You could go as high 14.5 without lights and be okay. With lights on, I don't think you'd want to be any lower than 13.5 at an idle. And the output should be pretty stable throughout the rpm range, plus or minus about half a volt. If you have got decent output at idle and the output jumps to 15, or higher, when revved, it's bye bye reg. Also, if your voltage doesn't go up past 12.5, it could be the reg or the alternator.
You could also have a phantom draw or a short draining the battery. A quick check on a bike without an ECU is to make sure the ignition switch is off and disconnect the ground cable from the battery. Tap the ground cable against the negative battery post. Nothing should happen. If you get a spark, you've got a draw somewhere in the system.
If it turns out that the reg is the culprit,(most likely) I'd suggest replacing it with a Shindengen mosfet unit.
http://www.roadstercycle.com/ It'll give you a very stable output, in the neighborhood of 0.1v. But they are spendy.