Ammeter to voltmeter

[Hotboat]

I would like to change the Ammeter on my old style Mercruiser to a Voltmeter. This would make my new gauge selection more versatile. Does anyone have a wiring diagram for doing this? I currently have a red/white wire coming from the alt to the ammeter and then to the ign switch on 1 post and a red wire coming from the battery/starter on the other post. Can anyone help? Thanks, Dale

[mattyboy]

as far as the voltmeter it just goes to + and - on the battery
the ammeter is different and needs heavy gauge wire

try this for the ammeter to make sure you disconnect the correct wires and don't have a live wire

http://www.sr20forum.com/technical-information-library/131404-how-install-ammeter-gauge.html

[Hotboat]

Hooking up the voltmeter is easy. My concern is the main supply wires coming to the ammeter. If I clip the red/white wire I have no juice on the ign switch. If I clip the red wire--I have no battery power to the dash. Maybe I am making it more complicated than it is but these wires must continue a circuit somehow.

[Mr X]

Just tie the red and white wire together.

[MOP]

An ammeter is a lot more useful, a volt meter just shows system voltage not system draw. So you ride along blissfully seeing all that good voltage not seeing a pssible odd overage of draw on the system indicating a problem. Welcome to La La land!

[b.guggenmos]

I would have to disagree. If you have a voltmeter and the engine is running it better be up around 13.5-14 volts or you have a problem. With the ammeter you might miss a low charge rate or low discharge rate depending on the state of charge of the battery and the sensitivity of the gauge.
A boat "generally" does not have a huge draw on the charging system so you may not see high rates of charge and discharge on an ammeter.
The ammeter may tend to stay near center.
But if you have a voltmeter and you start seeing voltage decreasing to less than about 12.5 volts you better start heading to shore because your alternator is not charging and the battery is going dead. Also you could catch an overcharging situation if the voltage got up near 15 volts and you would not know this with only an ammeter.
If you have room in your dash both an ammeter and voltmeter could prove usefull.
Brian

[Conquistador_del_mar]

I would like to change the Ammeter on my old style Mercruiser to a Voltmeter. This would make my new gauge selection more versatile. Does anyone have a wiring diagram for doing this? I currently have a red/white wire coming from the alt to the ammeter and then to the ign switch on 1 post and a red wire coming from the battery/starter on the other post. Can anyone help? Thanks, Dale

There is no need for all the current to come from the alternator up to the dash and back to the + terminal of the starter solenoid since you are not going to run an ammeter anymore. You can either disconnect the red/white heavy gauge wire at the dash that runs to the alternator and run a heavy jumper from the alternator output directly to the + terminal at the starter solenoid or just tie the two heavy gauge wires together at the dash and still run a heavy jumper wire from the alternator to the + starter solenoid post. If you disconnect the red/white wire at the dash, all the charging current will be running through the heavy jumper wire that you install, but if you tie the wires together at the dash, you will be running the charging current in parallel through the circuit to the dash and the jumper wire.
On my 1971 18' restoration, I also replaced the ammeter with a voltmeter. I preferred the simplicity of running a heavy gauge wire directly from the alternator output to the + terminal of the starter solenoid. I took out the original wire from the alternator to the dash and used the red heavy gauge wire that supplies the + voltage to everything at the dash. I honestly didn't try to make this sound complicated - lol. Make sense? Bill

PS
As another poster said, you could just tie the two (red/white and red) wires together at the dash. This would be easier.

[Ed Donnelly]

Both is better. Some of us have both stock from Donzi...Ed

[Hotboat]

There is no need for all the current to come from the alternator up to the dash and back to the + terminal of the starter solenoid since you are not going to run an ammeter anymore. You can either disconnect the red/white heavy gauge wire at the dash that runs to the alternator and run a heavy jumper from the alternator output directly to the + terminal at the starter solenoid or just tie the two heavy gauge wires together at the dash and still run a heavy jumper wire from the alternator to the + starter solenoid post. If you disconnect the red/white wire at the dash, all the charging current will be running through the heavy jumper wire that you install, but if you tie the wires together at the dash, you will be running the charging current in parallel through the circuit to the dash and the jumper wire.
On my 1971 18' restoration, I also replaced the ammeter with a voltmeter. I preferred the simplicity of running a heavy gauge wire directly from the alternator output to the + terminal of the starter solenoid. I took out the original wire from the alternator to the dash and used the red heavy gauge wire that supplies the + voltage to everything at the dash. I honestly didn't try to make this sound complicated - lol. Make sense? Bill
PS
As another poster said, you could just tie the two (red/white and red) wires together at the dash. This would be easier.
All of this makes sense, but what about the red/white wire that is feeding the ign switch from the ammeter post. If I disconnect it at the alt and use a jumper to the battery---then I will have no juice at the ign switch. Would I then feed the ign switch with the red wire????? That is the part that confuses me.

[Conquistador_del_mar]

All of this makes sense, but what about the red/white wire that is feeding the ign switch from the ammeter post. If I disconnect it at the alt and use a jumper to the battery---then I will have no juice at the ign switch. Would I then feed the ign switch with the red wire????? That is the part that confuses me.

Yep, your red heavy gauge wire will be the + supply for the ignition and other dash related needs. It will still be at the +13.5 or so voltage that the charging circuit supplies when the engine is running. This might be a good time to install a fuse or breaker panel under your dash since it probably has never been done if the boat is original - just a thought. I'm glad my post made sense. Bill

[Gerk]

I wanted to bring this thread back up as I am doing this exact swap.

In the back of the ammeter, there are red wires to switches and to ignition as well as the 2 large wires (one red and one orange) that go back to the engine.

I am going to wire the ground and the switch wires and the ignition wire to the new Voltmeter.
Where do the to large gauge wires go?
According to this thread it looks like they can be spliced together, but then where do they go?

I'm not sure why I am having such a hard time with this.

[mattyboy]

the way to think of the ammeter is it is inline with the main power circuit in the boat so elininating it would just mean splicing the wires but again it is heavy wire you don't want it shorting out on anything . the wiring on the vintage classics always scared me I rewired mine with a modern merc setup this may help see where the ammeter is in the circuit