Does it start with the blk/yel hooked up?
The blk/yel wire should provide ground to the switch box when the key switch is turned to the off position to kill the engine. If it will not start with the blk/yel hooked up, either the key switch is bad, the safety switch is bad, or the blk/yel is shorted to ground somewhere. One other thing it could be is the tilt mercury switch. The mercury switch should be on the side of the engine block, if yours still has it.
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