Wiring diagram for 12 volt with volt mater

[Roger G.]

I have a friend that wants to change an original Farmall H from 6 volt system to a 12 volt system with a one wire alternator and a volt meter instead of an ampmeter.
Looking for a wiring diagram.

Thanks for any help.
Roger
rjg15y@yahoo.com

[Bigdog]

Roger - tell him to ground the negative post of the meter and run the other post to the ignition switch wire that goes to the coil primary + terminal. The voltmeter will have voltage any time the ignition switch is pulled on.

[Gary Dotson]

Also, the wires that were formerly connected to the amp meter will need to be all connected together.

[Roger G.]

Thanks, BD and Gary for the replys.

Sorry guys, I forgot to say that the "H" has a magneto instead of a distributor.

Thanks,
Roger

[Bigdog]

Well, that changes things a bit. I believe a switch has to be added to disconnect the alternator to keep it from draining the battery when the tractor is off. I'll have to check and see if I can find a diagram somewhere.

[Eugene]

Instead of installing a volt meter, the easiest, less complicated, using the least electrical parts, cheapest, method is to use the amp guage. You may need to upgrade the current amp guage to match the alternators output.

[Roger G.]

Thanks Eugene,

I tried to talk him into using an ampmeter instead of a voltmeter, but his mind is made up on using a voltmeter.

I found a wiring diagram I think will work, but am concerned about the alternator draing the battery when the tractor is not running as BD suggested might happen. The diagram is one of Robert Melville's albums at, albums.photo.epson.com.

Thanks again for the suggestion.
Roger

[Bigdog]

For a one wire alternator to work all you need is a charge line from the alternator output stud to the battery positive terminal (or the lug on the starter switch) (this is a negative ground system)
Since it is a magneto system and he wants a voltmeter this is what I would do to make the system as efficient and easy to wire as possible. I would put a double throw toggle switch in place of the mag kill switch. Wire the voltmeter (+) to the hot side of the battery (+) and run the other side of the voltmeter back to the switch. Connect the center terminal of the switch to ground. Wire the switch so that when it is in the up (on) position the voltmeter is connected to the closed contact and the terminal from the mag kill terminal is connected to the open contact.
This ungrounds the mag and grounds the voltmeter (through the switch) in the on position. In the off position the switch will ground the mag and open the voltmeter circuit thus keeping the battery from draining back through the meter.

[Gary Dotson]

That's a good solution, BD! The tractor will still operate as before, without the need for a separate switch. I'm personally very much in favor of a volt meter over an amp meter. Monitoring volts gives much more information about the electrical system's condition than an amp meter, which only tells if current is flowing.