If a person has a 6 or 12-volt battery and several test leads, a preliminary ******** test can be performed without too much difficulty. If the ******** gives a buzz then further tests can be done using a spark plug and a high tension lead. Small electronic testers are available to test output and perform adjustments. Tools & equipment are available from model T parts sources.
If the ******** or coil components don't respond to testing then the dead coils will have to be repaired or exchanged for repaired units. I'm sure the model T club will have some sort of listing on repair shops for these old trembler coils.