Have you checked the safety switches? If in gear, the clutch must be pulled, and the kickstand switch is in play, too. So there are three switches here besides the starter button. Then the roll over/tip over safety switch must be good and in position.
Start by pulling the starter solenoid part and re-check the condition of the contacts inside at the end of the plunger. Then double check the starter button and kill switches. Move on to the clutch, gear and kickstand switches. If they check good, then check for broken wires between them and the ECU. The shop manual has good diagrams of the circuits, but it doesn't show routing which means you have to trace them. All this assumes the usual battery cables and their connections are sound. Try adding a second ground cable routed directly to under one of the starter bolts and not the engine block. This gives the starter an independent ground that you know is good.
I suspect you have a damaged wire where the insulation was abraded and then some of that Louisiana humidity corroded the copper inside. Tough to find but possible.