Installing volt gauge on magneto tractor

farmall pete · May 14, 2019

Anyone done it? Got an H with magneto ignition converted to 12v one wire alternator. Ammeter went bad & I have a spare voltmeter laying around. Scratching my head trying to figure out how it could be wired with the existing magneto kill switch.

rustyfarmall · May 14, 2019

The magneto is completely separate from the charging system. Do not even attempt to connect the 2.

A new ampmeter can be purchased at most any auto parts store and it will fit where the original was. Price should be very reasonable.

John T · May 14, 2019

Of course it has nothing to do with the magneto and basically wires across the battery to measure its voltage WELL DUH YOU SAY LOL. If you're thinking about some sort of a basic On Off switch so its connected ONLY when you run the tractor and you want to tie it into a Mag kill switch that's possible. Some sort of a double pole double throw toggle or push switch can be rigged so when ON the mag isn't grounded and the circuit from volt meter to battery is in place,,,,,,,,, but when OFF the mag is grounded out and the voltmeter is disconnected.

John T

bass · May 14, 2019

one on my M has a mag. the key is the switch.... I used a double point, double throw, normally off

farmall pete · May 14, 2019

Yes I am aware of how a magneto works. I know I can buy a new ammeter. Not interested in cobbling up another switch. Thought there may be an elegant way to do it. I have gotten pretty good at disassembling and repairing old ammeters. Guess I ll take this one apart and fix it.

Bob · May 14, 2019

Install a two terminal normally-open oil pressure switch and feed the power to the Voltmeter through it.

Or a relay powered by one of the alternator stator leads.

farmall pete · May 14, 2019

(quoted from post at 11:08:40 05/14/19) Install a two terminal normally-open oil pressure switch and feed the power to the Voltmeter through it.

Now that is an elegant solution! Thinking outside the box. Thank you.

Bob M · May 14, 2019

Possible easier solution: Wire the voltmeter direct to the starter "hot" post so it reads constantly, even when the engine is shut down.

Many (most?) voltmeters draw only a few milliamps of current - less than the internal leakage current of the battery and thus can be connected all the time.

Using an accurate VOM, measure the resistance across your voltmeter terminals. If it's more than about 2,000 ohms, you can safely leave the voltmeter connected constantly for MONTHS without appreciably draining the battery.

This is how the voltmeter is wired on my old Kenworth 10 wheeler. It can sit unstarted 6 months yet will start right up when I need it.

Installing volt gauge on magneto tractor

farmall pete

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rustyfarmall

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John T

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bass

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farmall pete

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Bob

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farmall pete

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Bob M

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