Ford went to 12 volt system in 1956. All the ones I worked on had a ceramic resister similar to GM. A few years later they went to a resistance wire that pigybacked the harness. They used a selinoid/relay that had an extra term. for bypass but some models used a bypass in the ign. switch. Coils that do not use external resisters do not have a resister built into it. They have more windings on the primary circuit thus giving it more resistance. This coil cannot cycle fast enough for high RPM multi cyl. engines so must be used only on low RPM &/or 1-2 cyl. engines.
