The fact that you said the headlamp doesn't dim and there is no voltage drop when hitting the starter switch makes a strong case in my mind that there is no current being sent to the starter. The starter switch closes the circuit, which allows current to the starter itself, which will cause a drop in voltage as it spins the motor. It it were me, I would get a jumper wire and bypass the individual switches one at a time. The kickstand switch would be the first one I would test, simply because it is exposed to a lot of crud and moisture. Someone mentioned the spring being weak and not holding it against the plunger fully. That is another easy check. You will find it, but it may take some time to trace!