What do I need to check? Truck will not start!

[Nickelcharlie]

Good Morning, I was driving my 86 GMC and it was running great till it lost power. I pulled over to the side of the road and tied to restart it. After the second attempt it would not turn over at all! It acted as if it had a dead battery.
Battery had over 12 volts.
Fuses under the dash check to be good with a test light.
In the past when the ignition module went bad the motor would turn over but there was no spark from a plug wire. Now the engine will not turn over!
Horn works. Headlights work but the windows and locks will not activate.
New starter. How do I check it? Do I have to remove it to check it?
Could the ignition module on top of the steering column be out of adjustment?
Any help would be greatly appreciated.