I am lost I took the engine out to repair front seal , put it all together ran on mag just fine Sat for about to weeks , Start it today would not run on mag 2 volts at post , I replace mag ring and charge magnet 4 months ago .
Sounds like a short or a ground in the field coil. A broken cotter pin or small piece of safety wire is a common culprit, especially in engines that have just been torn down and put back together. If you're lucky, you'll find it at the mag contact when you remove the post. If not, you will when you pull off the hogshead. If your luck is like mine, with that reading, you'll find it at about the 7:00 position in the field coil after you've removed the engine again.
If it comes to this, it's a real pain, and no fun, but it's not hard, and if it's any consolation, I had to do it on my '14 when, after installing and starting the engine, the magnets picked up a loose piece of a broken clutch finger cotter pin and inserted it into the field coil.
Start with the easy stuff first. Check for lint / junk on the mag post contact inside the magneto. That is a great place for lint to collect and lift the contact post off the solder button on the coil ring. If there isn't any there, then you can try the more complicated fixes.
I feel I have the same problem. Short of pulling the engine and removing the transmission, does anyone have a suggestion for any kind of flush?
Have seat, take a beer or two, think it over and try to find the problem. It is just a Model T.
You could run the coils on a 12v battery if the problem is severe. You can go a very, very long way on a 12v battery. Even if you start to lose it switch over to 6V. Very easy to do. That way you could enjoy the driving season and deal with it whenever you wish.
That is exactly what I did when my '14's mag went from 17.5 volts at idle to 2 volts.
When you do decide to pull the engine and fix it, pain in the rump though it be, the upside is that it will allow you to 'tend to other little annoyances such as pesky oil leaks and the like.
In my own case I replaced the low speed drum with a brand new one from Dave Nolting, bushed the pedal shaft holes so the O-rings would be more effective, re-bushed all the drums and the drive plate with NOS Ford bushings, repaired a stripped mag post hole thread, and of course cleaned the crankcase, etc., of sludge-like buildup (of which there was very little, but worth doing anyway).
Start with checking the small, simple things as has been suggested, but bear in mind that if you do have to go all the way it's not the end of the world; the original T system is well worth repairing.
It is possible that there is no problem with the magneto ring, but that somehow the magneto came in contact with battery voltage. That would de-magnetize the magnets. So I would try an in car recharge of the magnets before disassembling everything.
1.Clean mag post. 2.Try to recharge magnets on car. 3. Run on battery. 4. According to your profile, you have a 26, so it was made with a battery and generator. They will run on 6 volts except the top speed is not as fast on 6 volts. A 12 volt battery will give you more top speed, but is hard on the starter and the light bulbs will need to be replaced. I don't know whether 12 volts will damage the horn?
5. Remove hogs head and look at the coils on the top part of mag ring. 6. Remove engine and check all coils. 7. Replace with rewound mag ring.