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8 N Ballest resistor

Vince Mautino I have a late 1949 8N that had been converted to 12V.It has a 12V coil on it, new. I have been working on it since spring.
I won't start right away,but if I jumper it to the truck,it starts and stays running.

This morning while trying to figure out the problem I checked the voltage at the coil and it is 6.5 V, not 12 V. So I went back to the Ballast resistor. 12V goes from center bottom terminal of the ballast resistor to the ignition switch and the other wire from the ignition switch goes to the right hand terminal of the ballest resistor.The left hand terminal of the ballast resistor goes to the coil.

So the ballast resistor is cutting the voltage. from 12 Vto 6 volts.

If I jumper the terminal that goes to the coil, across to the center bottom terminal (12V in), the tractor fires right up, and if I remove the jumper, the tractor continues to run, only using the 6V into the coil.
Of course,I am non longer going thru the ignition switch so if I leave the jumper on, the tractor won't shut down until I remove the jumper.

Can I by pass the ballest resistor and just connect the ignition switch from the 12 V in, to the terminal that the coil wire is on so I have 12 V at the coil or will that damage something?

If not what is the proper configuration?

Thanks for the help

Jim Loveridge Yes you will damage the coil. a 12 volt coil is designed to run on about 8 volts or so and start on 12 volts. Go check out '' and click on the link to 12 volt conversion. He has some great information there. Keep us up to-date.
vince Mautino Tried to go to and there is a link for 12 V conversion, but it sends me to a Yahoo site with nothing about conversion.

Jim.Can you try that link and see what you get?

vince Mautino Tried to go to and there is a link for 12 V conversion, but it sends me to a Yahoo site with nothing about conversion.

Jim.Can you try that link and see what you get?

Vince mautino OK,I googled and got there. Found the two drawings with 1 wire and 2 wire alternators.
Neither one shows a voltage regulator and mine still has one.

The one with a 3 wire alternator shows another resistor in line. Would not that cut the voltage down even further.

Also there is no diode in line on my tractor.I don't know who converted this one.History is lost as my FIL bought it and I bought it when he passed away.

The alternator has never kept the battery charged all the way and I have to run the tractor at full RPM all the time. Low RPM and the battery gets used up. Can I fix the problem by putting a switch in that only allows 12 V to go to the coil when I start it.Like a momentary ON. Then let it run on 6.5 V when it is running?
Or should I just put a 6 v coil on it?

I am good mechanic, but a terrible electrician.

vince mautino Also on the drawing for the 3 wire alternator it shows a 1,2 and B. In assume the B is battery. Are the others Ground and Field? If so, which is which?
Jim Loveridge I had to use http://www.myfordtractorS (plural)dot com. I couldn't get there with just www. Sorry about that. I see that in his schematic for the 3 wire alternator that the voltage regulator is removed. That is a diode in that path, not a resistor, but he says you can use a 5 watt lamp instead. But here is the problem. You don't know what alternator was used in your installation. Those schematicks are for alternators with an internal regulator. If it were me, I would buy a G.M. 1 wire alternator and follow that schematic. Oh, A=ALT., F=FIELD and B=BAT. Maybe some of the other guys on here can help. I'm not really up on these conversions. 6 volts for me.:)
vince mautino Thanks Jim. I have aguy coming ov erSta to look atit who is prett sharp. Talking to him,the easiest thing for me to do is to put a momentary ON switch into the circuit that I can push on when I am starting it.
Fred Found this thread on 8N 12 volt wiring setup.

Here's my plan. I have a 1949 8N. I want to go the 12 volt route, but, keep the wiring as original. Remove the "points, condenser, etc, and install a Pertronix Ignitor kit in the distributor housing.NOTE: This will be part of my 12 volt change-over. Install a 12 volt round coil with a built-in resister. Install a 12 volt "B" circuit Voltage Regulator, Remove the 6 volt "fields" in the Generator, install 12 volt Fields. A 12 volt Battery with Negative ground.
I plan to keep the old original "Ballest Resister". NOTE: All this will wired up as those it is the original 6 volt system, with the exception...Electronic Ignitor...instead of points, condenser), 12 volt coil, 12 volt voltage regulator, and 12 volt generator fields, and 12 volt battery.

I think I can get this done and all is well working. And objections here? Or better ideas.

bob G You should have at the top of the coil with the points open pretty close to 12 volts. you may have a bad ignition switch. the resistor limits current flow when it is flowing. it sounds like the ballast resistor is wired right.try jumping the ignition switch and see what happens.
Vince mautino Bob.I have to give that a try of jumpering the ignition switch.

In the mean time,I put a push button switch to jumper across the ballest resistor to get me 12 V at the coil when I push it in to start the tractor. Without engaging that switch,I get aboutv 6.5 v at the coil.

I have been tring to get the charging circut operational. If I excite the Field of the Alternator with 12 V, it feeds the battery in about 17V with the tractor running. Without it, the battery reads 12.5V with the tractor running. So the altenator is working.

It looked like the voltage regulator was bad, so I bought another and it made no differnce. The regulator as 4 terminals, (Field), (A) for armature which is the Battery output coming from the alternator, ( S ),which I assume is the sensor that tells the Voltage regulator to the switch on and off. Another terminal is marked (I) ,I don't know what it is for.

I had to switch the wires opposite at the Ammeter as I was getting a negative reading . The std 6V system is a positive ground and the 12 V system is negative ground.

At then site, the wiring diagram shows feeding 12 V into the alternator Field all the time.I don't think that is correct as the battery would be recieving a full input cahrge all the time andI think it would boil the battery water away.
If anyone out there could shed some light on this I sure would appreciate it.


Vince Mautino I tried jumpering the starter switch. The original switch that is on the floor plate next to the gear shift shaft was defunct. The switch has been replaced with a push button switch up on the dash. That has only one wire going to the starter,which I assume just completes a ground to the solenoid.I actually got more voltage at the coil thru the switch that if I jumpered it.

I bet the original starter switch was a dual action switch that not only energized the starter, but also cut out the ballest resistor to feed the coil a full 6 V.

mark sr My NAA had the same starting set up you have when I bought it. Somewhere along the line I bought a correct replacement button from tractor supply. It only has one wire that goes directly to the solenoid. I don't remember the cost but it wasn't expensive. The factory type starter button will only allow the starter to engage when the tractor is in neutral.

I replaced that starter button back when my tractor was still 6 volt neg ground but have since changed it to 12 volt pos ground. I don't remember making any changes to the starter circuit.

Bob G
Re: 8 N Ballest resistor

I know of no Ford set up where the ballest resistor was by passed at start up. One wire went to the thumb switch and it provided a vround for the wire coming from the starter solenoid. when the wire is grounded the solenoid engages routing power to the tarter.
If you do not get the full battery voltage to the coil when the points are open you have a problem someplace in the circuit. I would check the connections on the ballest resistor if you are getting battery voltage when you jump around it. either that or replace the ballest resistor. You do not want to run very long with it bypassed. You WIll fry the coil.
The attached picture of wiring diagram is one of several for 12 volt conversions. Most alternators have a built in regulator and do not use an extral one. Not sure of what you have.

The wiring diagrams here for 12 volts do not show a VR.

vince Mautino Found most of the problem with the charging circut. The wire from the Voltage Regulator to the field on the Alternator was broken but showed continuity 2 out of 3 times I checked it.It must be broken but makes contact when it is moved.

I had put an extra wire in the harness to do some checking and by testing the original wire several times, I hit on the problem. So I cut the old wire out and replaced it with the new wire and now I am getting a good charge on the ampmeter and I have 12 V going into the field of the alternator.

I don't know what alterantor I have on the tractor,but suspect it might be old enough to not have an internal Volatge Regulator.

I only put 1 2V into the coil whenI start it up.Then I release the PB swicth and I am sending about 6.5 v to the coil. Once I get the battery full charged, I will try to do the starting with out engaging the PB switch. Should be OK since it has started all these years without the PB switch

The diagram you posted is what I have been loooking at also , butI really appreciate you taking the time to post it and think baout the problem.

Intermitent continuit is bugger to find.
Hopefully all is well now.

Thanks again.

BoB G Glad to hear you are making headway. let us know how the voltage to the coil comes out.
hank Suggestion...I have no idea how old this thread is but you can use the wire that feeds the starter solenoid to send 12 volts to your coil. When you stop "starting" the 6 volts will go to the coil as its supposed to. The 12v is for starting,.many older cars have two wires going to the coil, as start of 12 v and run volts lik6-9 after the ballast resistor.

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