The ballast will have higher ohms as it gets hotter and less ohms as it cools off. The hotter the ballast is the higher ohms it will have and the cooler it is the less ohms it has. Just curious as to how long the key was on without the eng running when you check the volts at the coil pos terminal ? I only ask because if its on a minute or two the ballast will start heating up and as it gets hot it will increase its resistance some. In other words as the car idles a bit the ballast wont heat up as much with the key on eng not running because the ECU is breaking the coil primary winding everytime it needs to fire a plug so at idle it wont have the current flowing thru the primary circuit which includes the ballast as long as if the key is on powering the primary coil circuit as long as it does without the eng running. That way when you are running the car harder at higher rpm's the coil and ballast cools more since the eng is running faster and the primary circuit is grounded even less time then at low rpm's and when ever the coil primary circuit is open (not grounded coil firing) it is cooling the ballast. And the cooler the ballast the less ohms it will have which will give the coil more output voltage avalible at higher rpm's. So the ballast might be .5 ohms with the car off and key off. Then with the key on for 2 minutes and eng not running it may read .8 ohms and then when running at high rpm's it may read around .5 again. Just a thought but I have see voltage from 5 to 8 volts on the coil primary + side with the key on and all ran fine. Ronb