1993 S-10 Blazer not starting

I have a 93 S-10 Blazer.  It has the 4.3L.  It had been starting and running fine till last Friday.  I wentto start it in the morning, and nothing.  It did not click or anything.  The battery is fine, i pulled it and had it tested.  I thought it may be the P/N switch.  changed it.  Next guess was ignition switch.  changed it.  Next was the starter.  (that was a pain to pull).  It bench tested fine.  I am running out of thing to try.  It has almost a full tank of gas, and I do hear the pump kick on.  I do not see any bad fuses.  I am open to any help.  Thanks in advance.

My truck is still not running.  I had not worked on it in several days.  I decided to warranty out the ignition switch.  Thought I may had a bad one.  Something strange happened.  I pulled the two plugs, and as soon as I plugged in the new one, the radio came on.  The key was not on, or even in.  So there is power to it from somewhere.  I was not ever grounded.  The blazer still does no start.  I did ground it, but but it is not mounted.  Any ideas?

check to see if you have spark and go from there.