I have a 91 loyale , a few months ago it would not  crank .( key on battery good) , I used a jumper wire on the starter  solenoid lug it fired easly so it wasn't the starter .   it would always start the first time  in the morning . after driving it would not crank . unless I jumped it. . so I installed a start button directly from the battery . all good.  for a month . now it will crank but not start .  im getting 8 volts at the distributor. when it cools down maby an hour it will fire .  I am thinking its the ignition switch .  any thaughts ?

  

I did replace the switch with one from a used car that was operating fine . 1 day no problem yet .

I had an 87 that had a similar failure. I replaced several switches but the problem kept coming back. Turns out the wiring harness to the connector where the switch plugged in had failed just past the plug. The harness was folded 180 degrees on itself durin asssembly. The largest wire in the harness is the 12V that switches through the ignition switch. The wire is a stranded conductor wire, and over time strands started to fail making the wire heat up, causing further erosion.

 

I spliced past that wire and fixed it for good

The fusible links that are located inside the small plastic box mounted on the coolant reservoir is another area that can cause this trouble. Check for loose connections to the links. The underside connections also.