The attached pdf is the circuit for the ignition system in millions of GM cars and also my Jaguar. It commonly known as a 4 pin HEI module and looks like this: http://tinyurl.com/2bjxqwx It limits the charging current to the ignition coil to about 5 amps. The driver darlington MJ10012 has a Vce(sat) of 2 volts. When the darlington conducts, it has 5 amps flowing through it and a 2 volt drop across it. That's 10 watts of heat to dissipate. I realize that is not an insignificant amount of power, but why does this thing run so hot you can't put your fingers on it?