93 Prostar 205 Speedometer Broke

[Avman2119]

How can I troubleshoot why my speedometer doesn't work? I know it doesn't work just need to figure out which piece of it doesn't work.

[Spork]

First, clean out the pitot at the aft of boat with a paper clip or like item
Second, remove hoses from pitot and the speedometer head, blow out hose with compressed air
Third, use a mighty vac and apply air pressure to speedometer head and see if it reads, caution a little pressure goes a long way you don't want to blow the diaphragm in the speedo head, if the boat has damper tubes, disconnect and work around those.
With doing these checks it should be easy to diagnosis and fix your issue.