Smoked HEI coil.

Grounding the coil wire might damage the coil driving transistor in the HEI module. It can be checked with an Ohm meter with ignition off, take HEI wire off the coil (-) , and check continuity to ground. If it measures less than 100 Ohms, the transistor is shorted and module is bad.

Yes the coil is likely damaged. The HEI circut limits the coil current to around 5A. By shorting the tach wire to ground, and no ballast resistor in the circut, the 0.5 Ohm high energy coil will reach 24A. That is about 5 times the normal current, and the coil will burn the enamel insulation and potting material after several seconds. When the tach wire removed, the coil kickback and current release damages the transistor. Energy increases as current squared, so if the current is 5x higher than normal the energy the transistor is absorbing in the protection mode is 25x greater, hence failure. In normal operation the HEI controls peak coil current, and is very reliable.