checked wiring harness, no corrosion; what readings do i need to take?
Firstly please note NEVER
start the bike then disconnect the battery - you will likely blow something up
First off disconnect the battery negative terminal and then check its voltage. Should be ~13VDC when fully charged, if its under 12.4VDC then hook it up to a battery charger until fully charged then re-test, if still below 12.4VDC then take it in to a shop and get it load tested.
Reconnect the negative terminal and start the bike. Now check the DC voltage at around 5,000 rpm with the high beam on, should be ~14.2VDC but below 15.5VDC.
If below 13.5VDC then read on. If above 15.5VDC then you probably need another regulator and a new battery. (worth getting it checked by a shop at this point cause batteries and regs aint cheap)
So, if you have less than 13.5VDC with the bike running you are not charging the battery properly hence you cant start, pull off the left hand side mid fairing under that you will find a plug with 3 yellow wires in it, disconnect it and check the resistance between those wires, it should be between 0.1 Ohms and 1.0 Ohm If its not then you need a new alternator (generator). If it is then you likely need a new regulator.
Other things to check before handing out money:
Check the AC voltage coming out of the regulator with the bike running, should be under 1VAC. If its not then new regulator.
With the ignition key in the OFF or LOCKED position then disconnect the negative terminal from the battery and place an ammeter between the negative terminal of the battery and the negative wire. This will allow you measure your leakage current which should be no more than 2mA, if its is then you need to disconnect the regulator and re-check. If its still over 2mA then your problem is most likely with the ignition switch otherwise - new regulator.
Hope all this helps and makes sense. I'm happy to clarify any points you are a little unsure on.