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Author Topic:   Tachometer wiring
flint99 posted 06-29-2001 06:06 PM ET (US)   Profile for flint99   Send Email to flint99  
Just bought (1 month ago) a 62 Eastport. Its in great condition I think, minor spider cracks in Gelcoat and some touchup on keel, but overall ok. Trim gauge works but the Tach and Volt gauges don't. Had tune-up on motor and the rectifier replaced. I tried to wire the Tach and got a pulse on it (so I think the gauge is ok) but still not working. Does anyone have a wiring diagram for this or all gauges...TIA for any info.
jimh posted 06-30-2001 01:13 PM ET (US)     Profile for jimh  Send Email to jimh     
Generally on older 2-stroke engines the tach derives its pulses from the same coil that provides current to the rectifier for battery charging.

The pulsating current from the coil (of referred to as a STATOR coil) enables the tachomoter to indicate crankshaft speed.
The tachometer will usually have a selector switch to match the tach calibration to the number of pulses per revolution of the flywheel, which is in turn determined by the number of magnet poles contained in the flywheel.

The tachometer also generally needs battery voltage and ground applied to it, and most also have another terminal for gauge illumination.

Measuring the tachometer lead with an AC Voltmeter will show about 12 Vac. This is because the 12-volt battery clamps the voltage output from the stator coil at 12 volts. Any higher voltage and the rectifier conducts current into the battery.

Six poles is a typical number, so at a rotation speed of 1,000 RPM, the tachometer lead should be producing about 6,000 pulses per minute, or 100 pulses per second. If you happen to have a frequency counter (often built into better Digital Volt Meters) you can count the pulse output.


daverdla posted 08-29-2001 04:31 PM ET (US)     Profile for daverdla  Send Email to daverdla     
Just found so useful info on teleflex's site regarding tach wiring.
Chris J posted 08-31-2001 11:46 AM ET (US)     Profile for Chris J  Send Email to Chris J     
I'd try to fix the voltmeter first. It's easy to troubleshoot, and the problems may be related (i.e., fix the VM and the tach may start working). I'm thinking you may have a bad ground at the gauges.

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