I have a 73 duster with a stock 318 and stock electronic ignition. I bought a new ballast resistor from Oreilly because the one on the car broke apart when I bumped it cleaning the engine compartment. When I checked the voltage at the coil it read just over 10 volts at idle and 11.6 at higher rpm

Isn't this too high?

I then checked the resistance of the new ballast resistor and it's .5 ohms. I thought it was supposed to be higher than that?

Thanks,
Ken

That is low resistance. The MSD one is .8 and usually the part store ones are around 1.0 to 1.8. I would want the coil voltage closer to 9v

If you checked the volts at the coil with the eng running then thats not bad. To do an accurate check you need to read the coil volts with the key on eng not running. Think of it like if you had points in the dist as the points do the same thing a transister does on the electronic ign. Anytime you read the volts at the coil + terminal it will read 12 volts with the key on eng not running if the points are open. Even with a 5 ohm ballast it would read 12 volts with the points open and eng not running. Now with the points closed then current is flowing and you should read about 6 to 7 volts at the coil + terminal with the key on points closed and eng not running. So when the eng is running it will read an average of the 12 volts and the 6 to 7 volts. See with the points open the voltmeter then would be hooked in series instead of paralell like it should be with the points closed and that why it will read 12 volts (battery volts) with the points open. Think of it like a garden hose with water flowing. If you put a restriction in the hose to slow down the flow you would be able to know about how much the restriction is with the water flowing out the end of the hose. Now close the valve at the end of the hose and the hose will just build up pressure and read the pressure since no water is flowing and you wont know what the restriction is. Thats kinda like what happens with the points open as no current will flow with the points open so you wont get a true voltage reading.

Let us know what it reads with the key on eng not running ? Ron

Ron,

I have 7.35 volts with the key in the on position but not running.

Thanks,
Ken