no spark

I have a mallory hyfire 6A with a HEI distributor. I am not getting a spark from the coil ? which also happens to be a mallory. When I shut down after cranking there is a spark? that makes the engine diesel a little. Ran a self check on the Hyfire and the ignition switch and they are fine. The coil is getting a -8volt charge when the ignition is turned to power not start ? is this correct ? minus 8?, and if all is good what is the best way to check my coil in case that is bad ? Really confused.