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Changing ampmeter to a voltmeter

Your old Chris-Craft electrical system can be a challenge. If it runs on "juice" pose your questions and offer your advice here.

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Changing ampmeter to a voltmeter

Post by johnnyeal » Mon Apr 09, 2018 11:30 pm

I am trying to confirm wiring
I terminated the wires to the ampmeter
Ran a new wire from the on post of the ignition to the positive post on the voltmeter and a new wire from the ground to the negitive post on the voltmeter
It reads 8 volts and not 12.6
Battery test at 12.6 with a multimeter on the battery post
Shunt, voltage regulator not bothered except to terminate the old ampmeter gauge wires behind the instrument panel

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Location: Eastern Massachusetts

Re: Changing ampmeter to a voltmeter

Post by mbigpops » Tue Apr 10, 2018 7:18 pm

Okay so what are trying to read on the voltmeter - battery voltage or running voltage from the alternator ?

If you want to read the battery voltage then you can connect to the ignition switch as that derives from the battery. If you want to read the alternator running voltage then you cannot connect to the ignition switch but need to connect a wire from the alternator to the voltmeter. This may have been the wire that originally went to your ammeter.

The other question is why are switching in the first place ? The ammeter tells you a lot more about what is going with either current draw or charging then just seeing what the voltage is at.

Either way is looks like you are dropping voltage from the starter to the ignition switch. You need to measure the voltage going from the battery to the starter to the ignition switch to see where you are losing voltage. Maybe the start relay ?

1953 CC Rocket Runabout "Rocket Man"

Denis D
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Re: Changing ampmeter to a voltmeter

Post by Denis D » Wed Apr 11, 2018 12:18 pm

Are you sure your Voltmeter is calibrated correctly? With the ignition on and the meter showing 8 volts, connect your multimeter to the voltmeter terminals to confirm the reading. If it is 12 volts then your Voltmeter is off, if it is 8 volts then you have a high resistance connection somewhere between the battery and the gauge which could be on the hot or ground sides.
BTW - When checking the voltage at the battery, put the leads on the cable clamps, not the battery posts as it is not uncommon to have a bad connection there. You should also have the ignition on so there is a load on the battery.

Denis D

1948 17' deluxe runabout

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