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Author Topic:   Mercury Tachometer
david537 posted 06-29-2008 08:49 AM ET (US)   Profile for david537   Send Email to david537  
I have a 2002 115 Mercury two-cycle outboard. Two years ago I replaced the stator and rectifier. I have been troubleshooting the tachometer. I discovered voltage from ground to the tach (gray) wire on the tach. I disconnected the plug-in wiring harness at the engine and from the tach; ohmed the wire to the tach. I checked each pin to make sure there were no shorts, none were noted. I disconnected the tach (gray) wire from the rectifier and checked continuity from the wire harness to the connector, checked good. I checked for voltage output (engine not running and swith off) from ground directly to the rectifier tach wire and read approximately 7 volts dc. Is this normal? Or do I have a bad switch box, rectifier, or starter solenoid? Note: the rectifier draws power directly from starter positive terminal. Thank You.
jimh posted 06-29-2008 09:30 AM ET (US)     Profile for jimh  Send Email to jimh     
If your motor has the rectifier and regulator separate, that is, not combined in one assembly, check the rectifier diodes.

The rectifier is usually a full-wave bridge with four diodes. Disconnect the stator lead from the rectifier and also the RED output lead. This should isolate the rectifier and allow you to test the four diodes individually.

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