GM-GMC: Wont start., turning the key, guessing game

Question
1986 GMC C1500 wont start at times.  It usually starts and runs rough for a minute then smoothes out and runs good.  Sometimes the engine turns over but refuses to start.  There is no spark to the plugs.  I do notice that when turning the key to OFF, the engine feels like it is trying to turn over for an instant.  I believe something in the distributor is failing.  What can fail and then start working again later?

Answer
In a couple of words:  Electrical parts.

GM had problems with ignition switches in the 1980s.  You may have a bad switch.

Or, you may have a bad ignition module, coil, distributor rotor, cap, etc.

You may also have a poor connection to any of the above parts.

You should take the vehicle to a shop for diagnosis to find out where the problem is.  Otherwise, it is just a guessing game.