Left my key on

The voltage measured, as you discribed is "Phantom" (it only exists because your meter is across an open switch and allows a small current to flow) The voltage will be ~ (about) the same with or without the Ballast R, but measuring voltage across an open switch does not mean your circuit is operational.

Measure the voltage across the coil, with points closed = >11 volts without resistor. The voltage across the coil with points open is ZERO...

JMHO

Ya can't just connect yer dwell meter from coil terminal to ground. Or from distributor points junction to ground. You'll get full scale dwell every time. 6 or 12, resistor or not. Dwell meter gotta be "across" the coil primary. Understand?

Theres been a ration of short spring thingies underneath the frontmount coil and need to be stretched to make good reliable connection to transfer sparkies to the distributor rotor button. I'd check there because all of your other testing implies that you are getting the correct voltages down inside your distributor.

This doesn't give the new 12 volt frontmount coil a clean bill of health because you could still have a bad secondary. You can and should check coil continuity with an ohm meter.

Off tractor, put one ohm meter lead on coil terminal, and then on the bottom terminals, read resistance. One terminal (primary which goes to the points) should read about 1 ohm. 'Tuther terminal (secondary which goes to the rotor) should read about 7000 ohms. MAJOR DIFFERENCE..... ....Dell

If the ballast resistor is removed from the circuit, then it is no longer possible to measure dwell at one of the coil terminals, since it is now at a constant voltage.

I suspect that Babalouie got used to measuring dwell in a way that was accessible and "worked" for him. Once the ballast was removed from the circuit, this could have stopped working.

After re-reading his post, and Dell's, I suspect Babalouie was not actually reading voltage "through the coil", but rather at the high side of the coil. The seeming inconsistency between the two tests he did (continuity vs. voltage) together with the inaccessibility of the point side of the coil connection, supports that.

The most likely thing is what Dell said. Something wrong with the secondary system like the coil spring terminal, the coil itself, or the rotor/distributor cap.

(Points burn/wear in normal service due to the arc created as they transition from closed to open.)

I believe that the front mount distributor, by the nature of its design, has a very large dwell angle -- much larger than the side mount or modern cars.

A properly sized alternator anti-backfeed diode should not have failed in this situation -- otherwise it would have burned out the first time you turned the key on to attempt to start the tractor.

It is possible that the coil and resistor were damaged due to sustained heating, although the typical "Chrysler Ballast Resistor" should have tolerated this.

One could argue that a properly designed 12V conversion should survive the operator leaving the key on; it happens often enough. But I can imagine a conversion reusing the original 6V coil, original "infamous" ballast resistor, and then using an inappropriate dropping resistor might have resulted in burning the coil and "infamous" resistor.

It should not be necessary to change distributor cap and rotor because of this -- unless you felt like changing them anyway.

With the engine stopped and the engine sitting with the points closed, it should be impossible to get 12.5V "through the coil". The points are a dead short to ground when closed.

There is an open circuit somewhere between the place you are measuring and the points themselves -- perhaps taking everything apart to change the parts you described you broke a wire or connected something incorrectly.

I'm not familliar enough with the mechanical arrangement of front mounts to suggest the best way to trace where the 12.5V suddenly transitions to 0V, but that is the best way to proceed.

Sounds like your coil isn't working, lucky you, you were able to find a bad one with which to replace the one you fried. Try another coil, maybe you'll get lucky and find a good one. Good luck.

Mike