I was working on my 09 Roadster on the weekend and have a question. Per the encyclopedia this is the style I have.
It was not working before I removed it and found the spring barely protruded from the bottom of the housing. Also the spring is so tight in there it can barely move. I pried the spring out some and now the mag works great. Did the John Regan test with 1156 light bulb and it puts out plenty of voltage. I didn't go past 10-12 VAC so I wouldn't burn out the bulb.
Does the spring get its electrical contact from the screw on the top or from the interference fit in the housing?
The top housing is a bored out piece of solid brass. The spring is conically wound not exactly as you have pictured since it gets gradually larger the higher up toward the top you go. The idea is that the top few turns of the spring are tight in the bore and that is a solid transfer of electrical contact between the bronze spring and the brass hollow end of the upper brass part. The mounted portion is made from hard fiber and insulates the entire upper brass portion from ground. The threaded portion on top is part of the one piece solid brass top. The entire upper metal portion of the contact is "hot" with regard to electricity and you will find that you can connect your wire to any part of the top brass housing, nut, or lockwasher and it will light up your test light. Ford added a center contact brass slug into the end of the spring and that was the next change to the magneto post. I make a repro of this post but I supply that center slug on all of them from 1912 on back through the beginning since it helps to keep the spring centered on the solder pile and is sharp on the end to sick into it. It is possible that someone swiped a spring out of a later one and put in there which would result in a poor fit but it is normal and correct for only the end portion of the spring to fit tight up in there and the bottom portion to move in and out of the bore slightly. It doesn't move at all once it is properly installed. Notice the small notch in the lower end of the fiber - that was part of the crimp that held the brass barrel down into the hard fiber portion. That was gone starting with the 1913 basic version and also with 1913 and later the fiber is thicker at the part you have labeled "thin". I think Bruce copied my drawings from my certificate of authenticity on this part which comes with the repros I make. Bruce of course had my permission to do that since we often researched together. I sure miss him. I never had a better pal and he made research trips a hoot.