Strange problem

Freddie2010 · May 7, 2023

Hi, I have a John Deere 420w 1957. I just changed it over to a 12volt negative ground system from a 6 volt positive ground system. When I turned the switch on the volt meter started to work. but then quit working. I checked the pole on the back of the ignition switch where I hooked the hot wire too, and I am now getting no juice to that pole ( connection ). Could I have cooked the ignition switch putting 12 volts to it? No one has ever mentioned changing the ignition switch to 12 volts . If anyone has any ideas, please let me know what may have happened. At one point when I was moving the switch from on to off and back. It would not shut off. Now it will do nothing. I appreciate any and all information and help I can get. thank you in advance.

Jim.ME · May 7, 2023

What was the total scope of what you did to convert it from 6 positive to 12 negative? Change to an alternator, etc.? You mention the voltmeter started to work. Did you actually convert to a voltmeter? If you did convert to a voltmeter, did you put a switched power wire to one terminal and ground the other? A voltmeter does not wire in series like an ammeter. If you wired it in series, with all power going through it as done with an ammeter, it likely has burnt up. Just a first guess based on what you posted.

Tony in SD · May 8, 2023

That was my first thought too. Amp meters are wired in series. Volt meters are wired in parallel.

BarnyardEngineering · May 8, 2023

Good catch. Yup, if you put a voltmeter in place of an ammeter, it will go "PIFF!" in about 1 second.

If you have a wire coming from the starter lug (or battery +) running to the voltmeter, and then a wire from the meter to the switch (and everything else), it's wired wrong.

Easy fix is to put an ammeter back in. You can add a voltmeter, but the way to wire it is to connect the + to the same side of the switch as the ignition coil, and connect the - to chassis ground.

The ignition switch doesn't care about Volts.

Jim.ME · May 8, 2023

(quoted from post at 07:30:37 05/08/23) Good catch. Yup, if you put a voltmeter in place of an ammeter, it will go "PIFF!" in about 1 second.

If you have a wire coming from the starter lug (or battery +) running to the voltmeter, and then a wire from the meter to the switch (and everything else), it's wired wrong.

Easy fix is to put an ammeter back in. You can add a voltmeter, but the way to wire it is to connect the + to the same side of the switch as the ignition coil, and connect the - to chassis ground.

The ignition switch doesn't care about Volts.

He has the same post going on the JD forum. The voltmeter is wired correctly based on a response there. Generator to alternator conversion, no real details on exactly how he rewired it.

used red MN · May 8, 2023

Jim, I have not looked at the post on the JD board but
FYI, just to realign your Monday morning thinking. If a
voltmeter used the studs for its internal connections
for reading voltage and it mounts with insulated pass
throughs on the clamp as an ammeter would the
following would be the result. He would not burn out
the volt meter, he would simply show battery voltage
on the volt meter and nothing would work because the
volt meter circuits do not have enough resistance to
power even a dash light. I have seen where voltmeters
have been used in the ammeter position and the mount
studs were not insulated and there was a dead short to
ground of the wires placed on the studs. Most of those
type of voltmeters have separate terminals on the back
to connect to for taking the voltage reading as shown
on the example gauge in the link.
Example volt meter

This post was edited by used red MN on 05/08/2023 at 09:06 am.

Freddie2010 · May 8, 2023

(reply to post at 05:48:05 05/08/23)

Ok, the studs are not insulated. But the positive and negative connections are below the studs. I have the positive going to a post at the back of the back of the ignition switch that is hot when I turn the rotary switch on. The negative post is going to ground. Is this correct.? thanks

Jim.ME · May 8, 2023

Yes that is correct

used red MN · May 8, 2023

Nope, no ..piff.. No different than wiring a dash bulb in
series in place of the ammeter, the bulb
would just light nothing else would happen. Same here,
the volt meter would just read volts. The more
important issue is that I believe most volt meters
are designed to use the studs only for mounting and
not for the meter circuit that reads the voltage. See
other reply.

This post was edited by used red MN on 05/08/2023 at 09:08 am.

used red MN · May 8, 2023

As others have replied in your post on the JD board
yes that is correct.

Freddie2010 · May 8, 2023

Hello, I am about to solve my problem. I have a mechanic coming out here next week. The deeper I got into this the more confused I became. I can't thank you guys
enough for all the help.

Freddie2010 · May 8, 2023

(reply to post at 16:54:56 05/07/23)

Hi again, I give up, The more I got into this problem, the more I became confused. I called a mechanic and he will be here next week to fix the problem. Thank everyone who tried to help. You guys have been great.

BarnyardEngineering · May 8, 2023

Well hopefully he knows what he's doing and doesn't charge too much. All too often it's exactly the opposite, sad to say.

Freddie2010 · May 8, 2023

(reply to post at 15:18:35 05/08/23)

I am sure you are right about that. All I can do is hope for the best. My neighbor had him fix his tractor and he was satisfied. I should be so lucky.

Strange problem

Freddie2010

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Jim.ME

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Tony in SD

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BarnyardEngineering

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Jim.ME

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used red MN

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Freddie2010

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Jim.ME

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used red MN

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used red MN

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Freddie2010

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Freddie2010

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BarnyardEngineering

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Freddie2010

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