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The switch works the same as the Mercruiser Alpha series drives.
If you look on your engine for where the shift cables are, they will attach to a shift plate. On that plate is your upper and lower shift cables, the switch lever, and the actual switch itself. You can't miss it, just look for the cables. Now have a look at this picture below.
What you do is simply use the tip of a screwdriver, with the engine running, gently pull the shift roller away from the V notch in the shift lever. The engine should stall if the switch works. The engine will do nothing if the switch is bad.
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