What voltage is on coil terminal on a 1940 9N tra

Couple of points. The "infamous ballast resistor" is a temperature controlled variable resistor. (that is why it is called a ballast resistor) When COLD its internal resistance is about 0.5-0.7 ohms for hotter sparkies at startup; and as it internally heats up, (takes about 2 minutes) it automagically changes resistance to 1.4-1.7 ohms for normal running. (even iff'n the outside temperature is below freezing or 100*)

Too many ill-informed shadetree mechanics "by-pass" the MANDATORY ballast resistor for hotter sparkies and eazier starting. Well guess what? within about 1 hr you have OVERHEATED yer squarecan ignition coil and melted its insulative tars and shorted out the primary coil winding and endup with permanently weak sparkies that will "cure" themselves overnite. (for just about 1 hr of running time the next day)

Unless you have a LAB-GRADE ohmmeter$$$, you CANNOT accurately measure your ballast resistor's resistance. (its a technical thing) But even the cheapest voltmeter can accurately measure the change in coil voltage that the ballast resistor effects.

2nd point. You MUST ISOLATE your switched alternator EXCITE from your switched ignition coil run circuit. GeneralMotors Chevy uses an idiot light to stop the alternator from BACKFEEDING internal alternator volts to the ignition coil. I know of 7-ways to stop this backfeeding 'cuz iff'n you don't, you won't beable to turn yer engine OFF.

3rd point. The OEM 6 volt squarecan ignition coil requires the "infamous ballast resistor". And iff'n you want, you can run yer OEM 6 volt coil on 12 volts by connecting BOTH the "infamous ballast resistor" and a 12 to 6 volt converting resistor (1.6 ohm chrysler resistor) in SERIES like flashlight batteries.

4th point. NO MATTER how many resistors yer coil has from the ignition switch. You still NEED somesort of isolation scheme (resistance) between the alternator and the ignition switch. Otherwize you can't turner off.

I really feel sorry for yer ol'timer acquaintance for NOT UNDERSTANDING the simple conversion techniques needed for his ol' N-tractor, and yet I'll bet he was quite proud of his "conversion"..... ...respectfully, Dell a 12 volt advocate for the right reason

That said, much to the annoyance of my teenage son, I haven't found the right reason to convert my eazy starting 6 volt 52 8N, and I know how to do it right, the 1st time.

2.2 volts at the coil terminal is TOO LOW and will result in weak sparkie's, hard starting, and missing.

And yes, yer coil spring thing is the "infamous ballast resistor", it usually fails like lightbulb, works or doesn't work. And while it is conceivable that the ballast resistor has increased its resistance (which is VERY DIFFICULT to measure, its a technical thing), its very eazy to measure the resultant resistance change as voltage at the coil terminal (with points closed). Iff'n you read 6.3 battery volts, yer points are open.

Remember the 6 volts MANTRA: "keep'em clean, bright, and tight"..... ....respectfully, Dell

If the voltage is good up to the switch side of the resistor, and drops across the resistor, you have a bad coil that is partially shorted and drawing too much current, or a weak resistor.

Roger in Michigan