Tach only works before engine fires

stubborn1

Cadet
Joined
Apr 12, 2007
Messages
7
87 Bayliner Capri 1750 2.3 OMC

I'm working on fixing some minor issues before hitting the water. When I bought this boat last year, the previous owner (who bought new) said the tachometer never worked for him. The tach will give a readout while I'm cranking the engine off the battery, but as soon as it fires the tach dies. Any idea what could be causing this?
 
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