I have a 1986 Mercury 6cyl 90hp...after winter storage (outdoors) it would not start. The starter would turn the flywheel but get no spark. I replaced the Stator, Trigger and rectifier. That did not fix it. I then unhooked the blk/yellow wires from the switch boxes as suggested and the motor STARTED! So then I replaced the key switch, no luck again....So what I have is a motor that will start with the blk/yellow wires unhooked but not otherwise.
Any suggestions on where to go next? The only thought I have now is the shift switch. My shifter is mounted seperate from the key switch.

It has a landyard emergency stop switch, disconnect it and retry. Check wiring on engine and going to key switch look for a short on black/yellow wire.

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