1979 K10, 400 sbc, Intermittent no crank.
It has only happened twice but I hate the idea of being stranded. It normally cranks like a mad man. I first thought it's the solenoid/relay switch but I don't think I could hear any click so I am now wondering if it might be the ignition switch. This last time it failed I started it and it cranked well and ran fine for around 20 minutes. I shut it off for about an hour and then when I tried to restart it nothing! The on position of the switch seemed fine, the dash woke up and the fan came on. I moved it to the start position, the fan stopped and no crank, release the key and the fan came back on. This repeated for about ten attempts. The battery voltage was well over 12 but I don't remember the exact value. I got a helper to turn the key while I read a voltmeter and it cranked quickly and started perfectly first try. Battery is relatively young and good with clean connections.
What do you think should be my first steps?
Edit, I should have added that my helper could see no dimming of the headlights when I turned the key to the start position.
Thank you for reading.