Fred Werring

Well-known Member
Converted an 8n to 12v 10 years ago. Bought a rebuilt 10si from Autozone.
My wiring was correct, used an idiot light, not a diode, had done a few other tractors so I had some idea what I was doing.
But never could get the alternator to start charging unless the engine was revved almost full throttle. Then it would continue to charge even if dropped back to idle.
Took it back, Autozone tested it, said it was fine. But I insisted, and got another one.
It did the same thing. Had other things to do, so just lived with it.
So the alt died this week, took it back (lifetime warranty) and got another.
It starts charging right away like it's supposed to.
Guess the rebuilder had a batch of off regulators when I bought the first one.
FWIW
 
The wrong size light bulb can cause that. Short across the leads and if it charges as it should you know it's the bulb
 
Short across the leads as in take the light bulb out of the circuit for a short period of time
 

Those alternators were originally designed to use with a #194 lamp. In some applications the lamp was parallel by a 10 Ohm resistor so the alternator would excite even if the lamp burned out.

A #194 lamp draws around 1/4 of an Amp of current.

An alternate lamp that draws less current than a #194 MAY not pass enough current to excite the alternator.

(That's why a typical LED indicator lamp won't work for this application.)

Do you know what lamp you have?

As to the alternators, they MAY have all been within tolerance for excite CURRENT needed, but still enough different not all will excite at low RPM's with the setup you have.
 
I have been using the same 1 wire GM alternator for over 30 years and do not have any method to "excite" the alternator so do not really understand the need. yes it need to reach some rpm before it starts charging. What's the big deal? Start it up, warms up a bit and drive off to do your chore. It starts charging. Current battery is from 2013 and no battery tender used so alternator must be working.
 
Hard to say what lamp I'm using.

They're from Radio Shack, somebody on this site (maybe not this forum) suggested them years ago.
Then I came across a deal on ebay and stocked up. Think they look like the pic.
Used them on a few conversions, never had an issue with them.

I'm just tickled it's now charging the way I thought it should have 10 years ago.

cvphoto145958.jpg
 
When I changed to an alternator on my 8n 20+ years ago I had the same problem. Finally figured out that the pulley I had from the old generator was too large. I went to a hardware store and bought the smallest 5/8 wide pulley they had with a 1/2 hole. I bored it out to the correct Id, installed it and alt. started charging at a little over idle speed.
 
Early or late 8N, you don't say. One of the major reasons for charging failure on these FORD's regardless whether if 6V or 12V is the lack of a fan belt tensioning device. Without proper fan belt tension the battery will never charge. With a 12V switch over, you also need to get the correct belt and replace the 6V battery cables with the correct 12V cables. The entire wiring setup must also be correct too -starter motor, ignition switch, ammeter, with no shortcuts. On the front mount distributor the OEM Ballast Resistor is needed with both the 6V and the 12V setup. On the later Angle (Side) Mount distributor there is no Ballast Resistor. With 12V whether front or side, you also need to add an external, in-line 1-OHM resistor in the coil circuit if using the 6V coil. Eschew the extra resistor by swapping out for a proven 12V coil - my preference - why add more stuff to get tangled up? Also with 12V some choose to swap out the Ammeter with a Voltmeter. I prefer to keep the OEM Ammeter for technical reasons - you want to see if the unit is producing AMPS, not VOLTS. Incorrect wiring accounts for 99.98% of all non-starting issues. Once all is right with the world, your best investment is a good float charger like the Deltran Battery Tender to keep the battery at full charge when tractor is idle and then ready to go when you are. Your basic garage trickle charger is not good. Some trickle chargers left unattended can overcharge the battery and boil out the electrolyte thus rendering it junk. You just can't refill it with more electrolyte - it doesn't work like that. BTW, I believe Radio Snack is no longer in business.




FORD 8N TRACTOR CORRECT 12V CONVERSIONS by JMOR:
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FORD N-SERIES TRACTOR BALLAST RESISTOR - USED ONLY ON FRONT MOUNT DISTIBUTOR WITH BOTH 6V & 12V:
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EXTERNAL CERAMIC 1-OHM RESISTOR REQUIRED WITH A 12V CONVERSION WHEN USING THE 6V COIL:
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DELTRAN BATTERY TENDER JR:
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Tim Daley(MI)
 
Did similar, bought a small diameter 5/8 pulley when I first changed it over.

When I was fooling with the not right alternators 10 years ago, and I took the first not right one back, Autozone would swap the pulleys.

When I took the dead one back last week, they said they didn't have the tools to swap it.

So I had to buy the new alternator, take it home, swap pulleys, and take the bad one back for a refund.

And I didn't remove the pulley before I went in, as I figured they would want to test it before they gave me a new one.
But their test machine was broken, had been for 3 months according to the store manager.
Couldn't seem to get corporate to fix it.
 

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