Replacement tachometer for a 1973 Mercruiser Thunderbolt ignition

donwhiteside

Seaman Apprentice
Joined
Oct 25, 2005
Messages
30
Hello all- My old Cruise-a-Home has a Mercruiser 325 engine with III outdrive. The ignition system is a Thunderbolt, with no other designation. I think it might be the original TBolt series.

The upper station Tach is toast. I have heard and read that this ignition system needs a special tach (too high voltage for normal tach??). In any case, I can not get a reading when attaching my diagostic tach to the (-) side of the coil, or anywhere else.

Suggestion? Source for another tach? Someone suggested an "in-line" resister to lower the voltage?

Hoping some of you old timers will remember this system and have suggestions.

Thanks in advance-

Don
 
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