Weird issue, new points and capacitor. Car will start easily on bat all four coils fire, switch to mag one coil goes dead. Verified by shorting at plug.
Did you switch the coils around to see if it follows the one coil?
Yes, I replaced the coil with a backup and it fires on mag no issue.
It may have an open wire in the windings. Maybe there is enough amps/volts to jump the gap on DC battery but not on AC magneto.
Get someone to test the out of adjustment coil on a hand cranked coil tester or a Strobe O Spark so that you can see what is wrong with it.
I'm having the same issue with two of my coils that were rebuilt maybe 3 years ago and had new points installed this past June. The whole set was sent out to Ohio, repointed, and adjusted on his HCCT. The first one died on the Finger Lakes Tour and the second went out a month later.
If the coil was a recent repro, it may have been one that was built to only run on 6 or 12 volts DC.
I bought 4 like that and they would short out on the higher Mag voltage and not work well at all.
Ditto to James. The ones like that have a rough, light color wood case. KW stamped on some of them.Lighter in weight than T coil. J. C. whitney sold these in the 60's and 70's. They don't run well on Mag. There was an article, IIRC in Vintage Ford or T Times about these coils.
Good comment, I forget this because I learned long ago to only use Ford coils as cores, so it doesn't happen to me again.
Those KW branded coils were sold by Sears, JC Whitney, and other retailers up through the 1980's. The windings are not as good as Ford windings, so even when you have a good working one they are somewhat inferior. There have been a couple different brands of aftermarket coils recently, not sure how they rate, but if you stick to original Ford coils then you won't have a problem.
The coils that came with my 11 are K&W with a date of 1953 stamped in them.
Perhaps you magneto is weak.
The OP didn't say whether the coils had been set up on a tester or just the parts changed out. If the points were changed and the coil was not set up on a HHCT ,et al, then that is likely the problem.
They can work OK if they are adjusted properly but they will never have the output of a Ford coil.
Philip, those are the newer coils to which we refer.
When I got one or more of those, I would get a hold of one of my gas engine collector friends and trade them for real T coils of other things I could use. I think those coils may actually work better on a gas engine than a T because they will work when adjusted to draw only about half an amp.