How to identify and reave 1983 Hobie Harken Main sheet System

Hi, I recently bought a 1983 Hobie 16 and am trying to figure out how to reave this Harken mainsheet system. Could anyone refer me to a video/ diagram? and whats the black switch in the second photo? Thanks!

(I tried to link the image from imgur, hope it works)

https://imgur.com/a/qMN40BI

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Dan McNichol
Hobie 16 1983
South Jersey
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dup post, please delete

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Dan McNichol
Hobie 16 1983
South Jersey
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