Volt meter hookup with 1 wire alternator

[402BIGBLOCK]

I installed a newer 1 wire alternator 100amp. I wanted to know how to be able to hook up the volt meter or will I have to go with a different amp gauge?

[Andy4639]

Voltmeter only needs a hot wire and a ground. The unfused of fuse black ground to the dash. Make sure both are good clean connections.

[Shyguy]

I don't think amp gauges will work with a one wire alternator.

Just a side note, I know a guy who has been working on these old trucks for a least 15 years that thought that the amp gauge in the dash was a voltmeter. When I told him it was an amp gauge and not a voltmeter he was surprised.

[OneOffStroker]

Yessir, voltmeter's don't give a hoot where the power comes from. Ground the (-) lead and apply ANY hot to the (+) lead and you're good to go. Your whole truck shares the same ~12 volts from the battery, so it will read the same everywhere.

[402BIGBLOCK]

Is the factory "Battery" gauge a volt or amp? How do I wire it up to work with the one wire(internal regulator) alternator?

[Andy4639]

Orignal question by 402BIGBLOCK.

I wanted to know how to be able to hook up the volt meter or will I have to go with a different amp gauge

A volt guage can be hooked up anywhere on the truck. It needs a hot wire and a ground that's it.
The factory guage is a amp meter not a volt meter.

[RichardJ]

Any analog gauge you find on a dash that has a "Center Zero" and says Batt or has "+" and "-" is a Ammeter. Often there are no graduations, because it is less important or would be confusing if the driver knew how much the generator is charging. The only thing that is important is that the needle has not swung left of zero or center and is discharging. Voltmeters are graduated, because it is important that the meter indicates more than 12 Volts and the majority of even blonde female drivers know that.

If you still have the original wiring harness and it didn't get too buchered up in the one-wire installation,then it should still look like the drawing below. At least the wires that are important to the Ammeter.
If the alternator worked before the alternator change, then it still should. The two fuses in the drawing go directly to the Ammeter and no place else.
The one fuse is located near the battery and on the radiator support. The other is somewhere near the original Regulator location behind the driver side headlight. The fuse holders are small rubber, hard to get apart and have a short glass fuse.
The section of Red 12R that connects to the battery "Junction Block" and the in harness junction with the other 12R wires serves as the "Shunt" wire for the Ammeter. The other 12R wires should still connect to the new alternator and to the firewall connector plug.
Start with checking both fuses.

[29od1]

I think the question he's asking is "What needs to be done to REPLACE the ammeter with a voltmeter for the 1 wire conversion?".

The 1 wire alternator conversion needs the resistance in the circuit that the stock ammeter gauge provides to operate correctly. If that gauge is substituted for a voltmeter, you loose that small amount of resistance in the circuit and it will eventually fry the alternator.

At least that's how I understand it. I'm also interested in the wiring change needed to do this.

[C5Phil]

Subscribed-- I want to install voltmeter too.....

[davepl]

The factory gauge isn't truly an ammeter; it compares the voltage between two points (the battery junction block and the forward harness). If it's higher at the battery, it shows "Charge" and if it's higher at the harness, it reads "discharge". The amount of variation determines how "far" the needle points.

It's pretty clever, but not all that informative. Then again, a voltage gauge tells you nothing about the state of the battery while the alternator is running. I prefer the ammeter so you can at least determine which way they current is flowing.

This whole discussion is somewhat separate from the three-wire vs one-wire alternator, but they are related. A three-wire alternator has a "remote sense" wire so it knows what the system voltage is back at the harness, not just at the main pole. I'd always prefer a three wire over a one-wire for that reason. Everything =except= my truck, which I'm keeping stock, I've converted over to internally-regulated, 3-wire setups.

[VetteVet]

This subject has been discussed many times on the electrical forum including how to wire the battery gauge and how to wire in a volt meter. There are some misunderstandings in this thread about the two gauges.
The older trucks before 1961 used an internal shunt amp meter and measured the total amperage used by the truck between the battery positive and the negative terminals. That's why the wires are so large on these older models.

In 1961 an on the factory introduced the battery gauge and changed to an external shunt which measures the voltage potential between the battery charge and the output voltage of the alternator. It is a volt meter but not in the true sense of the definition. It measures a small percentage of current in the battery alternator circuit and does not carry the total current between the battery and alternator circuits. This is the reason for the two small 4 amp fuses in the left and right legs of the circuits. They protect the gauge in case a break occurs in the charging current and the flow tries to go through the gauge. As Richard points out, it will show a left of center reading if the alternator output is low (discharge) and a right of center reading if the alternator output is too great and is overcharging the battery.

A true volt meter will read the actual voltage potential between the negative and positive points in a circuit. The battery gauge in our trucks reads the voltage potential in two points in the positive circuit.

The battery gauge will work fine on a one-wire alternator as long as the large output wire is connected on one end of the shunt wire and the battery is connected on the other end. See Richard's diagram. This is the same as the stock alternator wiring without the external regulator and the small plug wiring to the back of the alternator.
If the truck is the charging light dash type with three gauges then the charging light will not work and may be on whenever the key is on. If the dash gauge is changed to the battery gauge type the light will not be in the wiring circuit and the dash plug will have to be re-wired. Type "gauge conversion" in the search box and tick the 67/72 button and hit google and it will give you tons of threads on the subject.

A one-wire alternator does not need any external resistance from the light or an external resistor to operate. It is all done internally.

The newer style voltmeter can be wired between any positive and negative source and a keyed positive source is best.

[29od1]

That's great info. Thanks for your insight.

[Andy4639]

29od1 Volt meter hookup with 1 wire alternator
I think the question he's asking is "What needs to be done to REPLACE the ammeter with a voltmeter for the 1 wire conversion?".

The 1 wire alternator conversion needs the resistance in the circuit that the stock ammeter gauge provides to operate correctly. If that gauge is substituted for a voltmeter, you loose that small amount of resistance in the circuit and it will eventually fry the alternator.

At least that's how I understand it. I'm also interested in the wiring change needed to do this.

The voltmeter will not burn the alternator up if wired correctly.
Yes the ? is what does it take to hook a voltmeter up in the truck.

Hot wire from fuse block on/off ignition wire and ground it to the metal part of dash.

The volt meter has nothing to do with a alternator. It doesn't care if it's factory are 1 wire it doesn't matter it works the same.

Follow the wiring diagram for the amp meter.

Voltmeter


This is the aftermarket guages in my 71.
Voltmeter bottom left. The wiring is done by me.

[RichardJ]

Andy wrote;
The volt meter has nothing to do with a alternator. It doesn't care if it's factory are 1 wire it doesn't matter it works the same.
The same applies to an Ammeter. The one difference is that the Ammeter must be connected in a specific location. The Volt meter could be connected in virtually any location around the ignition switch, fuse panel, horn relay or cigarette lighter. The only criteria is that most people don't want it to operate when the ignition key is OFF. Go figure.

Vette mentioned that this truck uses an Ammeter with an external shunt.

ALL AMMETERS USE A SHUNT.

The first drawing is the Ammeter circuit. The 18 B wire goes to the ammeter and comes back out on the 18 B/W wire. The 12 R is the shunt and is in parallel with ammeter gauge. Current flows through both the 12 R and the gauge at the same time and in the same direction, except a lesser amount. The vast majority of the current flows through the 12R wire.

In the next drawing you see the 12 R wire again, but now it is used by the battery to supply all the current used by the truck. It serves two functions.
This circuit would look the same if it had a DC generator or int reg Alternator or ext reg alternator.

The third drawing shows what the ammeter circuit would look like if the ammeter used, had in internal shunt. All current used by the truck would go from the battery in the Black wire to the Ammeter gauge. All current would return on the Black/White wire to a junction near the DC generator or int reg Alternator or ext reg alternator and from there it would connect to the 12 R and pass through the firewall connector a third time to supply power to the truck. Yes, the Black wires would be increased in size. It's easy to see why they stopped using internal shunt ammeters for the copper alone.
The external shunt when used, just takes advantage of the natural resistance in the charge wire

The last drawing shows the brown wire that goes inside to the charge indicator light. This is the alternator exciter connection and has nothing to do with the ammeter circuit. There is no connection of any kind to the ammeter.

In my other post I wrote, "If you still have the original wiring harness...".
The only issue to consider when the alternator type was changed is if the 12 R was changed to a different size or length, because that would change the calibration of the shunt wire. A larger gauge shunt wire would have less resistance and a higher percentage of current would flow through it and less through the meter. For the same amount of current the meter would read lower than it should.