One thing we are experiencing with these 750s nowadays is: the Neutral Switches' contacts are getting corroded from long sitting and exposure to moisture. You can replace them with new ones, which are still being made because they are used in a Honda inboard-outboard engine for boats (Neutral Switch there, too). The switch can also be disassembled, cleaned (clean the little steel ball inside, polish it to remove the crud and rust) and reassembled, and re-sealed: use a good glue like Gas Tank Sealer (and work fast...) to do this part.
In both the K3 version (with the "safety module") and the later versions with the diode separating the clutch switch from the Neutral Indicator, the current thru the switch is very low, so just a little corrosion makes them stop working. The Switch is also in the bottom of the engine, collecting the worst grit, which doesn't help...sometimes I have fixed them by just cleaning them from the ball side with carb spray, spinning the ball and cleaning it. The ball is the contact device, as well as the tranny Neutral Detent and Switch actuator, all in one.