Spark

Ive repaced the coil three times in the past three weeks.I used an aligator clip on a spark plug to test the spark. There is a hair line spark.I thought it should be wider and brighter. I put my finger over it and there was a little shock, but I thought it should be more, so much more that I would have to pull my finger away. With the distibuter cap off there is spark at the points. New distributer car, rotor, points and condenser, also new plug wires. With the ignition switch on there is 8 volts across the positive and negative terminal of the coil. What do I do next?