Coil gets 12v from starter solenoid while starter is engaged and reduced volts from ignition switch after starter stops. Starting at coil,trace wire(s) back. If there's two wires on coil, one to solenoid and one to ballast resistor, the one on ristor is where problem lies. Make sure ignition switch is off, disconnect either wire from resistor then look for melted wire on resistor and check for continuity across resistor. Bad resistor is the most common cause of what you described but if previous test was good,trace wire from resistor back looking for broke or disconnected. When you reach switch,test for 12v with switch on. If still no joy post back. Questions?
