MTFCA Forum

I’ve been able to start on battery and switch to magneto with no issues until today.
I’ve checked all the obvious (to me) places, connections and post. Also took apart the switch and found nothing.
I started this morning and mag was functioning, this afternoon nothing.
What am I missing.
Thanks,
Bob

Pull the mag post & clean the lint around the contact spike. Might want to confirm a lack of mag output with an analog voltmeter first on the mag post directly.

In the 1980’s, after going over a rough railroad crossing, my T stopped. I started it on BATT and when I attempted to switch over to MAG, it started to stop, so I quickly switched it back to BATT and it came back to life, so I drove it home on BATT. When I got home, I discovered that the mag post point had popped off the soldered mag button. I sharpened the post point and straightened it and carefully screwed the mag nut on. When I tried it, it started on BATT and ran on MAG. Problem solved. Jim Patrick

Check the obvious things first. The mag wire going to and from the mag post. Make sure the connections are tight and making good contact.
Pull the mag post on top of the transmission cover and check for any lint or debris. Make SURE the spring that’s touching the soldered button on the top of the field coil is making a good compressing contact and in the center of the solder button.
It can happen when installing the post the spring gets pushed off to one side and eventually loses contact.

If your car stops on mag and after you switch the key back and forth and it starts running again on mag that could be an indication of a contact in the switch not working all the time.
The contacts in the switch have to have tension on them to work right. Try bending out the spring contacts for a better contact.

I installed a rebuilt engine in my T. It had all been done and the transmission and hogs head attached. Got it at the swap meet. It had been gone over by a good mechanic member of the club who was very familiar with Model T's. The first time I drove it the mag worked but all of a sudden it quit. I ran on battery for about 10 years and then I rewound three magneto coils and decided to install one in my car and see what was wrong with it. When I pulled the engine and hogs head. I found the funnel off the inside oil line laying in the bottom of the crankcase and the copper strips were cut. This happened because the magnets had rubbed the funnel. I also had a magneto oil line running down the outside to the front of the engine. Only oil I got to the engine was from the inside line without the funnel and the magneto oil line. The engine was fine after I had driven all those miles. I had even driven on the canyonlands tour for a week in Utah and Arizona. Up and down hills.
Anyway, something like that could have happened to your magneto.
Check end play of the crankshaft and also try recharging the magnets. If that doesn't help, you might have other damage.
Norm

My 1919 Roadster had the same thing happen to it, The new reproduction oil line funnel had come off and ruined the field coil. The funnel was to oval shaped and not flattened out enough to get enough clearance! It was OK for a couple of months and then one day the engine died and upon a closer look through the starter hole I just could see a copper strip hanging off to one side. And by the way it was new field coil I had installed. I learned my lesson about clearances!!

I had one pull a similar stunt on me once. It was the mag post grounding out internally. You’ll need to remove it completely from the hogshead to check it. Check for continuity between the post to the main body of the pickup.