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Author Topic:   Erratic Voltmeter Readings
seadog3 posted 04-28-2006 04:17 PM ET (US)   Profile for seadog3   Send Email to seadog3  
I have a 1995 75-HP Mercury. The voltmeter spikes to 18 volts intermittently. My warning alarm also goes on when the voltage spikes and goes off as it drops to normal. This started last season. This season I put in a new battery. Went all day without a rise in voltage, then. all of a sudden. it starts fluctuating again. This was during a very long choppy ride back to port. Also, my instrument lights work intermittently. There are three of them: gas gauge , tach and volt gauge. Sometimes only two of them work; sometimes one; sometimes all three. Also, the gas gauge itself seems to jump all over the place at times. Can all this be due to a bad regulator? Does it sound like a short somewhere? Which wires would I need to check to look for a short in the system?

Also, I ran the boat only once with the brand new battery and ran it just long enough at higher volatges to get back to the dock, about 10 minutes and it fluctuated at that. Did I destroy my new battery?

Chuck Tribolet posted 04-28-2006 04:33 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Your battery is probably OK, but keep an eye the water level.

Bad regulator or bad connection.


seadog3 posted 04-28-2006 04:47 PM ET (US)     Profile for seadog3  Send Email to seadog3     
Thanks chuck , but the battery is sealed. I just want to make sure I didn't cause any gas build up.
Bthom posted 04-30-2006 11:12 PM ET (US)     Profile for Bthom  Send Email to Bthom     
I had the same symptoms and found a broken ground wire in my control harness, where it flexes the most outside the transom.
Good luck,
AZdave posted 05-01-2006 01:41 AM ET (US)     Profile for AZdave  Send Email to AZdave     
I'm relating automotive rather than marine experience here, but I think the effect is the same. Voltage spikes usually come from the voltage regulator. This can kill batteries instantly. You may be able to clean the contact points in the voltage regulator. If the voltage is wrong, you may expect the guages to be wrong as well. I had a Ford with an extra regulator for the instrument panel. When that would fail, all the gauges would peg at maximum. Good luck in chasing this down. Dave
seadog3 posted 05-01-2006 02:47 PM ET (US)     Profile for seadog3  Send Email to seadog3     
Brian - where would I locate the control harness??
Bthom posted 05-01-2006 03:21 PM ET (US)     Profile for Bthom  Send Email to Bthom     
Sorry for being vague.
I was referring to the main wiring harness that carries all your instrument signals and controls to and from the engine.
It runs from your ignition switch to the engine and is a multi conductor cable.
Inspect it wherever it is accessible and look for breaks or chafe marks in the outer insulation. If you find any you may have to open it up and repair individual wires inside.
It is easier than it sounds.
You could also verify by putting a jumper from your instrument panel ground to another ground point behind the dash,perhaps on your fuse panel, bypassing the wiring harness ground.If things start working normally the problem is definitely your harness ground conductor.
Good luck,

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