I am not familiar with HEI but if it is labeled IGN then yes, it should be full battery voltage when the ignition key is on. But, what is that yellow wire for, and is it just hanging loose like that with a terminal connector waving in the wind?
By the way, I am adding this link, it is fairly accurate and was convenient for me to find. Notice the potential causes sections and especially the second item in that section. The third item in the section could be because your timing is off and therefore the car is running too hot, causing the problem. At any rate, I hope you can find the problem.
http://en.wikipedia.org/wiki/Dieseling