Re: 1992 Mariner 75 hp (3 cyl) need help!
you could try disconnecting the kill wire(s) from the ignition switch then start engine/check for spark... it may well help you isolate the issue. myself i would likely have a friend try to start her with the kill bypassed(disconnected) at the engine, and a wire connected that i could ground to kill the engine should i wish her to stop.
I know the last ignition switch i took apart had a star of david typ pattern to it... 3 hots, three grounds. it went...ground, hot, ground, hot, ground, hot... three hots 120* apart and three grounds 120* apart... it needed cleaning and relubing. you should be able to check your switch with a multi meter, remember to look for contack (ohms) between ea of the wires in all three positions of the switch. what mine did was essentially heat up the starter solenoid.battery (and had a spare unused terminal hot) to start, then to kill it grounded the coil to neg battery/block. very nice and simple. what i replaced it with was one that had choke included in the switch by pushing it, and it had a ton more connections. Just remember that unlike a car once the outboard is fired and running it needs no further input from the ignition switch or battery to sustain as it is a magneto system.
on that note lol, i have seen several people over the years try to put automotive ignition switches in their boats with dismal results and expensive repairs needed.
Sean