The normal voltage reading at the coil + terminal with the key on eng not running is usually around 7.5 volts when going through the ballast. As said most of the stock ballast I have seen were from about .5 ohms to about 1 ohm. Myself I have .25 , .50 , .75 and 1 ohm ballast laying around in my garage I have got over the years. If you try to read the voltage at the coil + terminal with the eng running its not an accurate reading because its just an average of the coil primary when grounded and ungrounded. When ever the coil primary is ungrounded (coil firing) you will read 12 volts (battery volts) because the circuit is not flowing to ground at that time and then when the coil primary is grounded it will read around 7 volts or so. That's why its best to read the coil volts with the key on eng not running at the coil + terminal which should be around 7.5 with the proper ballast but it will vary the longer the key is on as the ballast will get hotter and drop the voltage some. I run the orange MP ign ECU on my 63 and I don't use any ballast as I run a full 12 volts to the coil but I use the Accel super coil and it works good with no ballast because of the primary resistance in the super coil. I have been running my car about 5 years like that now but with a stock coil I would use a ballast with it. Depending on the coil and year car as to the exact ballast it calls for as the factory service manual will tell you. But I would shoot for around 7.5 volts checking at the coil + terminal with the key on eng off and check it as soon as you turn the key on so the ballast don't get to hot. If you get that then with the eng running at higher speeds the voltage at the coil will be a bit higher since the ballast will be cooler since the primary circuit has less time grounded at higher rpm and the ballast cools some and has less resistance when cooler and the coil voltage will go up some. Ron