Which is almost certainly the infamous ballast resistor. The reason that coil is a 6V coil, is that up until the mid-1950s, cars ran a 6V positive-ground electrical system. When the switch was made to 12V negative ground, coil manufacturers wanted to supply product that would still fit legacy applications. So, enter the ballast resistor. When you are cranking, full battery voltage (12V) goes to the coil, to assist in prompt starting. This very short duration does not damage the coil, but continuous operation would. So engineers put a large ceramic resistor (5W or 10W) inline between the ignition and the coil for operation while the engine is running. It drops the voltage to the coil to a safe level for long life. These resistors, being encased in a ceramic material, are brittle and fail in time. Then the car tries to start, but stalls when you release the key, as it switches over to the circuit with the (open) resistor in it. Cars with electronic ignition have a dual ballast resistor, so that the voltage is dropped a small amount on cranking, and a larger amount when running. If you put a multimeter across the resistor on the firewall, you will likely get a reading of infinity (open). Normal reading is a few ohms.