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Old 15 August 2011, 17:26   #11
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Originally Posted by doggypaddle

Isnt the alternator rotor the flywheel on a 9.9? and the stator inside it
Possibly, but the op is asking about a 75hp
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Old 15 August 2011, 17:30   #12
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Originally Posted by Polwart View Post
Possibly, but the op is asking about a 75hp
FEK got me posts mixed up
isnt a 75 the same though? seem to remember the stator has alternator coils and trigger coils for the ign module under the flywheel?
having said that the last 75 i worked on was 20 years ago.....
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Old 15 August 2011, 18:34   #13
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Originally Posted by Polwart View Post
Possibly
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Old 15 August 2011, 18:46   #14
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Silly boy Doggypaddle is showing his age. Modern 75 HP Mercury 4 strokes have belt driven alternators...
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Old 16 August 2011, 16:29   #15
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Silly boy Doggypaddle is showing his age. Modern 75 HP Mercury 4 strokes have belt driven alternators...

I did know that .........I missed the 4 stroke bit in the o/p must be a sign of getting old
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Old 18 August 2011, 13:09   #16
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Mercury rev counter

Hi,
Just want to say a big thanks to all that have posted their thoughts.

I'll start with the polarity switch at the rear, setting it to 4P then look at the wiring.

If all fails then it'll have to be a new gauge.

Thanks again everyone.

The Hoff
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Old 19 August 2011, 05:52   #17
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For polarity checking, buy yourself a 9.99 multimeter from Maplin, set the switch to "volts - any number above 12". Make sure the red lead is i nthe + terminal on the meter, black to - (if the meter has built in leadsthey wil lbe the right way round already)

Now touch the probes against the two marked "ign" and "gnd", red to "Ign", black to "gnd". Your needle should go to somewhere around the 12V mark on the dial, or if it;s digital show a positive number n the scale. If the needle tries to jump off the scale or you get a -ve number, the supply is wired @rse about face.

Next job: Follow the wire connected to "send" & check every connector between tacho & engine. It should finish at a small black or grey box with three or four terminals, two of the other wires of which dissappear under your flywheel the other will probably be a red which makes its way to the big cable from the battery. The wire from the tacho should be on the same connection as one of the wires from under the flywheel.

Note that was an educated guess about how your engine is wired. If it's a nice shiny new computer controlled thing the chances are that will all be done in the engine management box, so shout back if it doesn't look like what I described.
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