Coils?

Iwas just wondering what would cause a starting coil to fry on a newly rebuilt engine. I have gone through two coils in the course of a few months. I am thinking it could just be bad luck, but could use some advice.

 

If it is a 12V Chev, did you install a resister before the coil?

 

It's in a 12 volt Ford(390 v8) and there is a resister installed.

 

Is it the ignition coil or the starter solenoid coil. ?