Spark when key is turned to the off position?

Big_John said
It isn't grounded, but if it's just hanging by the wires, that can cause some issues.

If you have a ballast resistor with 4 connections, this sounds like the .5 ohm side of the ballast is burnt out (or broken) . This is a pretty typical failure for the symptoms you describe in your first post. Since your car is a '73, I would expect to see that type of ballast resistor.

What happens is when you turn the key to "start", the current runs through the .5 ohm side of the ballast. When you release the key and it goes to "run", you are using the 5 ohm side of the resistor.

So... If your ballast is just hanging by the wires, there's a good chance the resistor on the "start" side broke.

If you have a ballast resistor with only 2 connections, pay no attention to what I just typed.

Sorry this is not true. At least not as you explained it. One side of the resistor supplies the COIL and the other side supplies the ECU. THAT is the half that was deleted. The coil side has never changed so far as the circuit. IN FACT if the ECU goes bad, you can pull the ECU connector, drop in an old points distributor, hook the dist. to the coil NEG and if the ECU was the only problem, it will run

When you START the car with a 4 terminal ballast, "things are a trick." There is no "ignition run" power during start, the coil PLUS is powered through the ballast bypass (brown, IGN2) circuit. So the power BACKFEEDS through the resistor to power the ECU during crank. VERY POOR DESIGN in my opinion

Here is the circuit. The "ignition run" at lower right is DEAD during cranking. Only power to the circuit comes from "Ignition 2" pink in the diagram

Current flow from coil is from ECU ground, through box switching transistor, to coil NEG and through coil, out coil + and back to battery through the pink "ign 2"

Box circuit is from ECU ground, out pin 1, through resistor from right to left lower section, out resistor and back to battery on pink

Other section is s from ECU ground, out pin 3 (blue) to top section of resistor, through top section from left to right, through bottom section from right to left, and back to battery on pink.

This is "properly described" as neg to pos electron flow