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Author Topic:   Voltmeter Not Working
johninfl posted 01-26-2009 06:34 PM ET (US)   Profile for johninfl   Send Email to johninfl  
The voltmeter is not working and this is what [I] found so far: battery has 12.4-volt when engine [2003 Mercury 90-HP] off and 14.1-volts when running. I found two yellow wires that are getting hot located right at regulator-rectifier. The [tachometer] stopped working first, then voltmeter would read lower and then finally stopped altogether.
jimh posted 01-26-2009 08:12 PM ET (US)     Profile for jimh  Send Email to jimh     
There is not much that can be repaired in a voltmeter. I suggest you check the voltmeter to be sure it is really malfunctioning. It may not be reading because there is no voltage applied to it. In that case, the problem is not the voltmeter.

Electrical conductors which become hot are usually a sign of too much current flowing through them.

The tachometer is driven by the half-wave rectifier tap. If there are no tachometer pulses, that is usually a sign that there has been a failure in the battery charging circuit. Typical failures are the rectifier or the alternator winding (which is often called a stator winding).

Electrical diagnoses requires you to have an independent measuring device to make voltage, current, and resistance measurements. The service manual for your outboard motor will have a well thought out procedure which will describe exactly how to perform a check of the battery charging circuit. With a good multi-meter and the service manual, you will be able to perform an investigation and locate the source of the problem. My experience with the factory service manuals is their instructions are written for people who possess very limited knowledge of electrical circuitry, so they should be very easy to follow.

95Outrage17 posted 01-26-2009 08:47 PM ET (US)     Profile for 95Outrage17  Send Email to 95Outrage17     
If your 2003 Mercury 90-HP is a FOURSTROKE model, I suggest you visit this thread:

A failing part such as the regulator-rectifier could explain the problem with your gauges. It is a common failure on that vintage and size Mercury motor. It could also lead to a dangerous fire hazard.

- Chris

jimh posted 01-27-2009 01:50 PM ET (US)     Profile for jimh  Send Email to jimh     
Electrical conductors designed to be used on marine apparatus generally have insulation rated to at least 105°C. A conductor located under the flywheel of a motor may use insulation with an even higher temperature rating since it will be subjected to an elevated ambient temperature.

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