Starting my first Model T, 1924 Touring with starter. Magneto is not working, magnets dead and replacing with charged ones. Question is, the mag coil has continuity all around but there are several places where the insulation is wore off exposing the copper. Should the coil be replaced or will it be all right? The car has been running off a 12 volt, and I am putting it back to original. I do have the engine out,[along with everything else],would appreciate any help.
If the engine's out, it's poor economy not to replace an original field coil. The wrapping tape has become brittle and pieces are liable to fall off and clog the oil tube. In addition, there is metallic sediment in and around the windings, causing shorts that will reduce the mag output and which can even shift or cut through the weakened insulation and short the entire mag. With the copper showing, it's a no-brainer. Replace it and enjoy the reliability of the original dual-source ignition.
There are a couple references in this thread of excellent coil rebuilders. http://www.mtfca.com/discus/messages/257047/295118.html R.V Anderson being one of them. I wouldn't put an engine back together without having a re-condition coil ring.
I agree with the others. The mag coil is in there "way too deep" not to replace it while you have everything apart. If you put the old one back in and it doesn't work, you'll need to tear everything apart all over again to replace it.
Age takes it toll on an original field coil and its insulation. Kind of like an original radiator.
If you want to drive and enjoy your T and have confidence in it those two parts are almost a "must do".