Warwick's post on the ignition system got me to wondering. How many electrical connections are there on a T magneto ignition system? There are at least 18 on the field coil alone.
Secondary question: There are several places where a single disconnection could render the car inoperable, but how many connections could fail and still have the car be drivable?
For the sake of this exercise I would say at least three cylinders would need to be firing to be drivable.
When I picked up my car for the first time I got it on the trailer with 2 cylinders running. I just put it on the trailer and took it off running like this, then I fixed the coils and got it running on all four.
I drove mine home once about 7-8 miles with only two coils firing. I don't think it would have made it on one. She wasn't setting the world on fire with two dead, but it pulled itself home.
I only see two connections in the field coil. One, the grounding of one end, and the other is the solder puddle that the pickup mashes against. Other than that, the field coil is one continuous ribbon.
That's 2. (3) is the wire on the pickup. (4) is the other end of that wire, to the terminal block. (5) and (6) are the wire from the terminal block to the ignition switch. Ignoring the internal connections inside the switch, (7) and (8) are the wire from the switch to the coil box. (9) takes you to the bottom of the coil. Again ignoring the internal connections inside the coil and timer, (10) through (17) are the 4 wires from the timer to the coil box, and (18) thru (21) are from those studs to the coils themselves. Twelve more take you from the coils, thru the studs, to the plugs. I get 33 connections, not counting internals of the ignition switch, timer, and coils themselves.
Yes, that's a lot of possible failure points.
As to the other half of your question -- how many can fail without rendering the car inoperable? For the sake of simplicity, I'll say it only takes one -- # 7 or #8. But the exercise of naming the ones that could fail and still get you home, is a multi-variable equation.
Well, I guess I was talking internal connections too, as they can fail. The field coil is 16 individual coils, each has two soldered connections.
Tom is right to include all the connections on the field coil. A permanent soldered connection is less likely to fail than a removable mechanical connection. However on an early car without a battery and running on mag, any field coil connection that fails stops the car. And we know that sometimes happens if some foreign object slings around and damages the coil. So all field coil connections are potentially fatal-takes only one. External connections are prone to loosening, corrosion and high resistance buildup. The switch is most problematic as the contacts are sprung and movable.
I refuse to directly answer the question asked and wait for Tom's expert analysis (I'm lazy).
I am in a hurry so I didn't read everything, did you count where the coils touch the connectors inside the coil box?
The ignition coils also have a number of electrical connections, both inside the tar and the ones with the points on top the coils.
I do not know where Tom is coming from with regards to failed connections and still have the car drivable. Perhaps some people can drive the car with only one cylinder operating.
Then again if one is going down a very steep hill, I guess you could consider the car drivable even if the engine is not working, provided you have steering and brakes and a very long hill that you are going down and not up!
We will have to wait for Tom's "words of wisdom" in 2013. Perhaps he is giving us a brain teaser for 2013!
I would like to know the number, but it is a daunting task. It took me a couple of hours to figure out the number of connections in the field coil, and I probably got it wrong. Then there is the mechanical connections inside the motor. The field coil to the block, the block to the valve spring, the valve spring to the retainer, the retainer to the keeper, the keeper to the valve, the valve to the tappet, the tappet to the cam lobe, the cam to the timer rotor. Or does the electricity flow through the bearings? Or timing gears?