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Discussion Starter · #1 ·
1940 9N converted to 12 volt system. New 12V coil, distributor, points, rotor, resistor and all. New alternator, battery.

Rewired it this morning because I thought it wasnt charging. Now, after re-wiring it, it does the same thing.

When running and when putting a voltage tester to the battery (positive on positive, neg on neg), it only reads 6.5 volts. Turned off, the battery reads 12.5 volts.

However, when running and reversing polarity (negative tester lead on positive battery post), It reads 13.5 to 14 volts.

What gives? Is this tractor positively grounded? Should I try swapping the battery cables?
Is it possible that the 12v coil i have has a built in resistor?
Can I just bypass the resistor? If so, how? Just hook the existing wires that run to the resister in with the ignition?

I appreciate any feedback. This one has me stumped.

thanks,
Luap
 

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Discussion Starter · #3 ·
Not sure what to say..I am no expert on this.

I have "heard" that a 12V coil can be run without the inline resistor.

Take it for what it is worth..

Would it hurt anything to run as is for a while? Are these postive ground systems?
 

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A 12 Volt system is negative ground with the alternator. Run the big alternator wire directly up to the positive post on the battery.

The Key switch, switches the coil on and off.

Do you have the one wire or three wire alternator?
 

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What you are saying makes no sense at all. A 12V battery that ever showed as low as 6V would never crank the starter in the first place. I think either you've got a flaky meter, or didn't get it well connected. If not that, I don't know. This is not rocket science. There ARE coils made to run without resistors, you need to go to the source (store?) where you got this coil and find out. Virtually all 12V CARS and LIGHT TRUCKS from the first 12V to present run either a ballast resistor or "resistor wire" in the harness. This means that they are not truely "12V coils" they are "12V with the proper resistor" There are OTHER "general purpose" (industrial and tractor) coils sold that are designed to run directly off 12V.

Can you post a diagram? If nothing else, draw it out, take a photo, and use "tinypic" http://tinypic.com/ to post the diagram.

Ammeter, doesn't the tractor have one? Basically, ONLY the battery connects to one side, everything else, gen/ alternator and all loads, come off the other side

Alternator? single wire (I hate those things) Three wire? How is it wired.


Wrong ground polarity? Take a **** of a good look at the battery and cables. There's only ONE right way to run a 12V system, and that's negative ground. Was the battery every COMPLETELY dead? It IS possible, if someone is a complete "tool" to discharge a battery and then charge it back up the wrong polarity.

Find another meter. Find a friend. Take some more readings, and make SURE This is not rocket science. It's tractor science. I could do this when I was 13 years old. And I did.
 

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Discussion Starter · #6 ·
What you are saying makes no sense at all. A 12V battery that ever showed as low as 6V would never crank the starter in the first place. I think either you've got a flaky meter, or didn't get it well connected. If not that, I don't know. This is not rocket science. There ARE coils made to run without resistors, you need to go to the source (store?) where you got this coil and find out. Virtually all 12V CARS and LIGHT TRUCKS from the first 12V to present run either a ballast resistor or "resistor wire" in the harness. This means that they are not truely "12V coils" they are "12V with the proper resistor" There are OTHER "general purpose" (industrial and tractor) coils sold that are designed to run directly off 12V.

Can you post a diagram? If nothing else, draw it out, take a photo, and use "tinypic" http://tinypic.com/ to post the diagram.

Ammeter, doesn't the tractor have one? Basically, ONLY the battery connects to one side, everything else, gen/ alternator and all loads, come off the other side

Alternator? single wire (I hate those things) Three wire? How is it wired.


Wrong ground polarity? Take a **** of a good look at the battery and cables. There's only ONE right way to run a 12V system, and that's negative ground. Was the battery every COMPLETELY dead? It IS possible, if someone is a complete "tool" to discharge a battery and then charge it back up the wrong polarity.

Find another meter. Find a friend. Take some more readings, and make SURE This is not rocket science. It's tractor science. I could do this when I was 13 years old. And I did.
Roadrunner, I know. It is a strange deal. It's a brand new batter and when I test it with my meter (not running) it shows 12.5 volts. Start the tractor, do the same test and it shows 6.5. It's also a brand new alternator (3 wire).

The tractor does have an amp gauge. I put a new ceramic resistor, 12v coil, points, distributor cap, plugs, wires and rewired it this morning because it was doing the same thing before and I thought it wasnt charging.

Here's how it's wired up:
- one wire from alternator F connection to coil and then wired to one side of the ceramic resistor
- one wire from post on alternator with jumper to R on alternator to the amp gauge
- one wire from other side of amp gauge to starter solenoid.
- ignition to other side of resistor
- ignition to solenoid
- Solenoid to starter

Another weird thing. With the ignition on (engine not running) I can take a reading at the top of the coil and it reads 11 or more volts. Fire up the tractor, and it drops to 6.5 again.

Tested it without the resistor and got the same exact scenario. Makes no sense at all to me.

I am no rooky with mechanicing, but admit that wiring can be a challenge...on something new. Geez, this thing is 69 years old and only has 2 main wires. Should'nt be that tough I know.

Thanks for anything else to try,
Luap
 

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Your wiring is wrong... nothing from the alternator should be hooked to your coil. The charging circuit should have one wire form the amp to the battery terminal on the back of the alternator.

On the 12SI the two terminals are usually labeled 1 & 2 with the one cloest to the battery terminal being 2. That is to be wired to the battery terminal. Short jumper, it is voltage sensing for the regulator.

The 1 terminal is the exciter, it should be connected to an idiot lamp going to the ignition switch or is available an accessory terminal on the switch or even a momentary contact switch like a push button. Once the alternator is excited it will charge until you shut the engine off. REMEMBER this MUST be isolated from the ignition or you will NOT be able to shut off your engine.
 

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Discussion Starter · #8 ·
Your wiring is wrong... nothing from the alternator should be hooked to your coil. The charging circuit should have one wire form the amp to the battery terminal on the back of the alternator.

On the 12SI the two terminals are usually labeled 1 & 2 with the one cloest to the battery terminal being 2. That is to be wired to the battery terminal. Short jumper, it is voltage sensing for the regulator.

The 1 terminal is the exciter, it should be connected to an idiot lamp going to the ignition switch or is available an accessory terminal on the switch or even a momentary contact switch like a push button. Once the alternator is excited it will charge until you shut the engine off. REMEMBER this MUST be isolated from the ignition or you will NOT be able to shut off your engine.

I'll look at that tomorrow. Do you have or know of a diagram I could use. The one I found was a little confusing.

Thanks,
Luap
 

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Ya got problems.. and one of them is a cheap auto ranging digital tester that don't like points noise I'm betting.

Also.. the machine was originally positive ground.. your alternator is negative ground.. if you don't have the alt and the battery hooke dup that way.. the alt is ALREADY toast.. it won't tolerate swapped polarities for more than a few milliseconds.

soundguy

Roadrunner, I know. It is a strange deal. It's a brand new batter and when I test it with my meter (not running) it shows 12.5 volts. Start the tractor, do the same test and it shows 6.5. It's also a brand new alternator (3 wire).

The tractor does have an amp gauge. I put a new ceramic resistor, 12v coil, points, distributor cap, plugs, wires and rewired it this morning because it was doing the same thing before and I thought it wasnt charging.

Here's how it's wired up:
- one wire from alternator F connection to coil and then wired to one side of the ceramic resistor
- one wire from post on alternator with jumper to R on alternator to the amp gauge
- one wire from other side of amp gauge to starter solenoid.
- ignition to other side of resistor
- ignition to solenoid
- Solenoid to starter

Another weird thing. With the ignition on (engine not running) I can take a reading at the top of the coil and it reads 11 or more volts. Fire up the tractor, and it drops to 6.5 again.

Tested it without the resistor and got the same exact scenario. Makes no sense at all to me.

I am no rooky with mechanicing, but admit that wiring can be a challenge...on something new. Geez, this thing is 69 years old and only has 2 main wires. Should'nt be that tough I know.

Thanks for anything else to try,
Luap
 

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Here's one "proper" way to wire up a Delco alternator

and as posted earlier:

It MUST be neg. ground CHECK IT

Jumper no2 to the battery OR RUN a separate wire from no2 to the battery. This is the "sense" lead

No1 IS IMPORTANT. It must be hooked to switched ignition THROUGH A LAMP OR DIODE. This is because no1 can "feed back" and try to feed the ignition on shutdown AND ALSO there is an electrical situation whereby the internal circuit of the alternator can "try" to be the charging source OUT OF the no1 terminal. You MUST have a resistance or diode to stop that or you'll burn up parts inside.

 
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