40,000 volts to ground.
Sounds like what is happening at the spark plug.
I believe your box should have a white wire as well as a a green and purple with a plug to go in to your distributor or crank trigger. White wire is for a points style distributor.
Blake and orange are to the distributor, small red wire to switched ign source. 10 gauge red and black to a direct 12 volt battery source.
I will presume your ignition is wired per the above.
Hook up a spark plug to the coil wire and toggle the 12 volt switch source on and off. If your box and coil are good you will get a spark.
I do not believe you will see 12 volts at the coil.
If no spark, verify 12 volts at the 10 gauge wires.
Try subbing a known good coil. Continue to toggle the on off switch to the box. If still no spark, pretty good chance something happened to your MSD box.
Any chance you can get a MSD tester to try.
Like already stated, I don't think there are any parts inside that the average guy can replace or test.
Send it in to MSD or tech west for repairs.
While searching for the techwest web site I found this link: http://techwest.ipower.com/page2.html
. It might be of some help to you.
Best of luck in finding your problem.