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Tachometer for a 1977 Merc 50 hp

8

870xprs

New member
" My boat's shift/throttle

" My boat's shift/throttle control has a small covered electrical plug on the front that I assume is for a tachometer. I just bought the boat, a 1977 Lowe 1664 jon boat with a 50 hp Merc. Is that plug really for a tachometer? It has three insulated contacts (prongs) inside for positive, negative and ground???

Anyone know where I can get an original 1977 Mercury tachometer to plug into the fitting on the shift/throttle control? Would an automotive tachometer work just as well? What should the rpm's be at full throttle for a 50 hp?

Thanks

870xprs "
 
"Mercurys are not my line of e

"Mercurys are not my line of erpertise, however those tach plugs (at least the ones I've seen) connect to the tach in the same manner. The three contacts are: Positive (12v+), Negative (12v-), and the third one is a lead from the charging system that sends pulses to the tach. These pulses are what affects the tach with a change of engine rpms, resulting in the related rpm change of the tachometer. Sorry I can't help you with your other questions.

Joe
"
 
"yes, the plug in front of the

"yes, the plug in front of the control is for a tach harness. You can buy the harness from your local Merc dealer still. It is p/n 84-46239A1. No, an automotive tach WILL NOT work correctly, since it receives its signal from the coil and outboards receive their signal from the stator assy, sent by pulses. You can use any outboard marine tach with adjustable pulse settings on the back of the gauge. Max RPM's for your 50hp would be 5500.

Daren

"
 
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