The voltage is OK. If you checked the ignition coil primary voltage with the ignition switch in START, it would be 12 volts.
Any electric circuit can get too hot if the resistance (ohms) is too low. So, if the spark plugs, and wires, are supposed to have a certain amount of resistance; but, the resistance is much lower, excessive current will flow through the ignition coil, and it will heat excessively. Check the ohms of the ignition coil, spark plugs, and spark plug wires. Replace if too low, or too high.