what is the volt meter measuring?

84EdH

Chief Petty Officer
Joined
Apr 30, 2011
Messages
575
I have a 1979 century with boat side original wiring. I repowered the boat with a 5.7 engine and thunderbolt 4 ignition. When I view my dash voltmeter it reads about 12.5 or so volts. If I run the blower with engine about 1500 rpm the voltmeter drops a bit. If I add lights etc a bit more.

I verified the accuracy of the dash guage with a digital meter. Then with engine running again I used the multimeter at the positive and negative battery terminals and find a healthy
13.4 to 14.0 that varies with rpm (all below 1800 rpm on muffs)

Does this make sense?
 

agallant80

Commander
Joined
Oct 25, 2010
Messages
2,328
Re: what is the volt meter measuring?

Perhaps the meter is not connected to the battery directly?
 
Joined
Mar 27, 2010
Messages
3,008
Re: what is the volt meter measuring?

Probably have either corroded terminals or a worn/undersized power and/or ground wire running up to the helm from the battery, if your showing a large difference between the helm gauge and the battery itself.

Boats in '79 didn't have all the electronics we have today, something to think about. Although we don't know what your's has in it.

Your alternator should be able to handle the blower and lights running without a whimper, so my guess is either corroded ends or the wire itself could use an upgrade. I ran new 8-gauge (I think) power and ground wires to the helm which each feed a terminal block. then the accessories/ignition switch run off the block.
 
Last edited:

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
Re: what is the volt meter measuring?

The voltmeter measures the "electrical system voltage". But where the gauge is taking the measurement can affect the accuracy of the reading. Since you verified the voltage at the battery is in the correct range, the fact that the voltmeter is located many feet from the alternator and battery and is measuring low, confirms that you have a wiring issue or an inaccurate gauge. Every connection in the electrical system between the battery, engine and the gauge can present resistance to current flow and hence lowers the voltage beyond those points. Since the voltmeter is powered from the ignition switch, all of the connections between the gauge, ignition switch and back to the engine need to be inspected. If you read `13+ volts on the "I" terminal of the ignition switch with the engine at about 1500 rpm, then the problem is between there and the gauge, or simply a bad ground at the gauge or at the ground connection. Put your voltmater on the "I" and "G" terminals on the gauge and compare readings. If they don't match, the gauge is the issue.
 
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