Let Me Down Today

[MrBlue]

Greetings and Happy Father's Day,
Well today started out with good intentions. One of the other cars in the family fleet needed rear brakes. As I already had the rotors and pads, I thought this was an easy change. Well one of the caliper brackets slide pin was frozen.
Call to the local bone yard to locate the part.
Thinking it is a nice day, why not take the 72'.
Trip there was without issue. BUT when I was ready to leave, the truck would not start. It was cranking fine, but did not sound like it was firing. Added some gas to the tank, still no go.
Took out a spark plug and could not see any spark. Bummer.
Popped the HEI cap up and just pushed on the wires at the module. Reinstalled the cap and the truck started.
This is not the first time this has happened. Everything in the distributor is basically new.
Any thoughts? I do not like it when I am sitting there feeling foolish.
Thanks,
MrBlue