We love pictures!
And you came to the right person there with buckaroo. He's got a '77 too and has been around and under it a time or three.
And from the sound of it, it just stopped instantly? Didn't cough or sputter like it was running low on gas or anything?
Anyway, lots of things to check with the ignition. Right from the switch on the dash, to the wires, to the module and even the trigger in the distributor. Those things are super reliable, but now after 40 years they seem to be the culprit in more than just a few cases.
You're going to need to be testing a few things it seems.
Did it fire right back up and get you home at least? Or is it dead in the water still?
Good luck.
Paul