As you’ve discovered that switch is very expensive, I’d look for a used on on eBay. I had the exact same issue, on a 1991 Johnson, 8hp. the 8hp setup looks simpler to access the switch than yours. If it’s being used in a sailboat, & you don’t require the man-overboard lanyard, a generic switch should be fairly easy to rig up. That little C clip (part #16), simply keeps the spring loaded end from closing, which grounds out the ignition.
I got a used switch from a member here, then disassembled the switch, & simply replaced the little red end. That might work for you. The end of this thread shows how it was done.
I have a smooth running ‘94 Evinrude 8Hp, but have been on the lookout for a spare prop. I came across a farmer who had tossed this ‘91 Johnson 8HP in the scrap pile. Said he lost the water pump & overheated. Sat in his shop for a couple years, his kid went to look at it & said it was seized, so...
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