That wire is one of two that connect to the two "M" (magneto) terminals on the ignition switch. The black wire with the connector that was disconnected probably came disconnected when you were poking around behind the instrument panel. With that wire disconnected you would not be able to stop the engine with the ignition key or the kill switch. You should find a mating connector for that wire. Any outboard ignition switch with six terminals and push to choke feature will work. The letter identification on the new switch will be: B = Battery POS. C = choke/primer, M (2 of them) = magneto, S = starter, A = accessory (feeds the instrument panel). It will be active with the key in the RUN position. That terminal may also be labeled "I" for ignition but on an outboard with a magneto ignition system it is identical to the "A" function.