This is just MY experience with this problem:
1st was a no crank no start 2 years ago solved by replacing the starter (ignition) switch in the steering column. (Not the key-Ignition Lock Cylinder)
I tested voltage at the starter and relay found none when switch was engaged. Simple...
2nd was in 2019 till now, an intermittent engine cranks no start condition typically after overnight rain. The next morning no start, later in the day started normal. This increased to not starting when going home after work-again in damp weather. Hmmmm.
Testing voltage at the fuel pump seemed logical because the relay clicked.. voltage present at fuel pump... but this was a new AC Delco pump...and worked with a 12 volt supply jumper wire...
Then I remembered why I replaced the ignition switch. In that switch were a set of contacts that pitted and failed.
Here is my fuel pump relay. Bottom line... voltage with no amperage. (I bent this arm out to show the pitting.)
New AC Delco relay, back in service.

 

Nice sleuthing and very educational for the rest of us. Thanks for sharing your success. These followup posts are super helpful to people.

 

Nice, thanks for posting. I had a no-start condition in damp weather (overnight) too, and it ended up being condensation in the distributor cap.

I'm considering wiring a kill switch to my starter relay. While I'm at it I'll check the contacts on the fuel pump relay too.

Btw, I just ordered a new OEM ignition switch yesterday, and while I'm in there I'll be bypassing the passlock with a resistor (the reason why I'm wiring a kill switch for the starter).
The ignition components on these trucks are well known for failing at the worst time, lol I'm just trying to lessen the odds of getting stranded. I'll be keeping the old ignition switch/wire harness as a spare