The ignition system on the Model T was very peculiar - even for the time, with a low tension magneto giving power to one coil per cylinder. The magneto didn't give many volts when cranking or at idle, so the trembler coils had to be adjusted to work at the worst possible circumstances, without giving double sparks or misfiring.
Before 1913 this wasn't really sorted out, so many accessory master vibrator coils (what are these?) were sold to give the T a smoother running engine. Later coils were developed so they gave a more even spark, but they still needed regular service since the coil points wore out and needed adjustment. There were simpler devices to test coils, but only a hand cranked coil tester with a flywheel magneto (nice one on the end of the bench, anybody know of one for sale?) can test for double sparks, so the old testers are still in demand among current model T enthusiasts, even though a modern electronic device (the Strobo-Spark by Fun Projects) has been developed in recent years for the job.
Electric starting was developed for the 1912 Cadillac ( I think I just read about a manufacture who supplied one before Cadillac) and became common on other cars soon afterward, though not until 1919 on Fords. Closed cars were standard equipped with starters from then on; the coupe and Fordor in the picture seems to be of 1923-1925 vintage, so they had starters - though every Model T had the hand crank in place too, all the time.
photo & information copied from Shorpy web site
Montgomery County Motor Co
A HCCT can be built using scrap T parts for less than $150. It will work the same as the factory unit.
I would like to find reproduction castings to build my own or a HCCT needing restoration. Would also consider one in great shape for an unreasonably cheap price.
I have been trying to determine how long a set of coils will last without touching them. The set in my 15 was done by Ron Patterson about 13 years ago. They have run about 21000 miles. I might rotate the spare under the back seat, it has not been used.
Maybe in some areas coils might the coils might stay adjusted longer because of prevailing weather conditions. I find that every so often I need to recheck mine. My T is not in a climate controlled environment so atmospheric conditions do change the coils over time. In the summer the coil wood dries out and gets loose changing the settings, in the winter the wood swells up changing them again. Every so often I put them on the HCCT check and adjust as needed.
I've also wondered how often coils need to be adjusted. My car runs excellent and free starts are easy to come by. But like anything related to performance, it is hard to know how much you are leaving on the table. Is that reason enough to invest in a coil tester? Haven't been convinced of that yet.
Model T coil point adjustment is far more sensitive than most realize. Just a gentile bump is enough to significantly alter the time to fire spark retarding ignition by several degrees. This is very easily verified using an instrument capable of accurately measuring the Time it takes the coil to fire spark when a fast rising pulse of electricity is applied to the coil from rest.
A change in engine performance may or may not be perceivable depending upon the many variables which all contribute to ignition timing including Timer contact to contact variation, Timer position, CAM/Crank gear variation, spark plug gaps, cylinder to cylinder compression, etc.
For example, a misadjusted coil with coil firing time retarded by 2 deg may go totally unnoticed using a timer with +/- 5 deg of timer contact to contact variation. The coil point adjustment variation is not the limiting factor in such a case. This is what makes meaningful performance comparisons difficult and can lead to incorrect conclusions.
I'm with Royce. Get Ron or Brent to go through them, and you won't have to mess with them for a long time!