A molded rubber water proofing covering the rear of the coil box and insulators. Went between the box and firewall. About 1/8" thick. Old,real rubber, so age unknown. Did not do much good in a downpour! Limped home....
Yeah, but somebody bit.
I believe the purpose of this device was to prevent the coilbox wood from getting wet.
Coilbox wood getting wet is a problem today and, I believe a very prevalent problem in the Model T era. If this device prevented the wood from getting wet it would have been a good choice.
If you have ever trouble shot a wet coilbox,I can assure you (trust me on this)it is an experience you will not soon forget; if you touch the car you may feel a mild shock, the plugs spark, but with less intensity and the car runs very poorly. Finding the cause; carbon tracks in the coilbox wood is not easy to isolate and even after drying the box out it will still run poorly a because carbonized wood is still conducive.
Today, the best solution is to entirely dispense with coilbox wood and install the FunProjects wood replacement kit and be done with the possibility. No wood to get wet and it is easy to dry out.
Ron the Coilman
I also have the remnants of one of those accessory coil box "stay dry" units - yea, right !