Resistor Check 9N

I am re-ringing an 8N for a neighbor and he has it converted to 12 volts side mounted distributor. the odd thing was that he had installed a ballast resistor for the coil but instead of putting it in the circuit coming from the ignition switch to the coil he had the risistor in the circuit between the points and the coil. It ran is all I can say! I don't know if this could possibly reduce the voltage to the primary windings of the coil or not but all I know is that it would run!!!!
I am putting it back in the proper circuit before I try to start the enging when I get it back together.

Another unusual think I saw today was the ignition wiring circuitry on a 31 Model A Ford car. I would have thought that being so much like an N they ignition wiring circuit would be much the same @ Hot wire from the ignition switch to the risistor to the coil. Points to the coil circuit. Not so. The ignition switch is in the circuit between the points and the negative post of the ignition coil and the positive post of the ignition coil is hot all the time. This the way the wiring schematic shows it and the way the wiring harness is made and it runs too!!!!
What blew my mind was the fact that the primary winding in the coil is attached at one end to the battery at all times and is hot. When the switch is closed and the points make contact is the only time their is any current draw.

JMHO

I think I will get a coil tomorrow out at my shop and look at it with an OHM meter to determin just how this can be or is.

Phil

And the correct voltage reading depends upon wheather you have a frontmount or a sidemount ignition system and you didn't say. And unfortunately for you, I flunked mind reading, just ask my ex-wife.

But for your direct enlightenment, 9.5 or 10 volts on any 6 volt coil is much, much, much too high. Wheather you have a frontmount ignition or a sidemount system. It will burn out your ignition coil.

Trust me on this, most readily available ohmmeters really are not too accurate in the low ohm ranges, specially when you try to read less than 1 ohm. Howsomever....even the cheepest voltmeter is accurate enuff. Its just the way there made. And besides that, to read ohms you must have one end of the resistor waving in the air so that you don't have any ground loops, and/or hidden parrallel resistances.

Oh, and by the way, if you have a frontmount coil, you will need 2 resistors connected in series, like flashlight batterys..... .Dell

The 6 volt frontmount ignition coil requires about 3.5 at the coil terminal with the points closed (2.5 min, 4.0 max) and battery voltage with the points open. Anyother voltages is going to give you sparkie problems. This is accomplished with the infamous "ballast resistor" in the original 6 volt scheme.

Therefore, based upon what you have just reported as the voltage at your 6 volt frontmount ignition coil as being about 3 volts, you're right in the ol' ballpark.

As for your 10 volts on the far side of your conversion resistor, that is what I would expect at the junction between the OEM 6 volt "ballast resistor" and your 12 to 6 volt converting resistor (that came with your conversion kit) that you must have installed between the ballast resistor and the 6 volt frontmount ignition coil. And you probably don't even know it.

HOWSOMEVER...if you are absolutely certain that you don't have the original ballast resistor mounted on the backside of the dash panel, and will swear in Henry's name to all that sacred, that it is not there, then I'd be concerned that your ignition switch internal contacts are gunkin' up and providing a hidden resistance that is going to bite you. Old Ignition switches are notorious for doing that.

Eazy check, make a short jumper wire with alligator clipies on both ends and jump across the ingnition switch leads, if your ignition voltages increase, then you know what to do, replace the ignition switch.

Oh yes, the converting resistor, I'll really bet it reads about "zero" ohms, not "open" because if'n indeed it was open, you wouldn't read any voltages at the ignition coil at all. And the reason it reads about zero ohms is as I said, most common ohm meters don't read very accurately at less than 1 ohm, which is what the typical 12 to 6 volt converter resistor usually is..... ..Dell

Key On - Engine Off
Battery - 12 volts
Alternator - 12 volts
Hot side of resistor - 11.5 volts
Coil side of resistor - 2.5 volts
Coil - 2.5 volts

Key On - Engine Running
Battery - 14 volts
Alternator - 14.5 volts
Hot side of resistor - 13.5 volts
Coil side of resistor - 8 volts
Coil (measured very carefully) - 8 volts

So thanks again - I think I'll drink a cold one and review the formula for Ohm's law (not!). Till next time...

You can measure as carefully as you want but it still has "NO" meaning.

Jmho

I'm more concerned that he is reporting a voltage drop across his ignition switch. I'd recommend that he replace it before he comes asking why his tractor will only run for about 15 minutes and cuts out and won't start again without waiting for an hour or so..... ..Dell

The Voltage Vs Current characteristics of a particular Ballast Resistor need to be plotted and the corresponding resistance values calculated. This was done for the Standard N ballast, about 2 years ago, and the results were posted on this Board. The most important point in the graph is the 2.4 Amps brick wall (@ 1.75 ohms to ~ 2.4 ohms).

It can be determined that you require 2 Standard ballast resistors, in series, for a 12 Volt Front Mount. The voltage at the Coil will be ~ 2.4 Volts, with point closed.

Measuring voltages, with a meter, with the tractor running is meaningless in the ignition circuit. You need a Scope as the important characteristics are in the lowest values(minus battery) of the waveform. JMHO