Good people of the forum, I inch closer and closer to resolution on my no-crank-at-key condition.
Dale E had me run another test. He had me ground one of the control pins in the crank relay and test crank with key. Jackpot! So now we know it is definitely a ground issue and not a voltage issue, a start logic issue, or any issue with engine codes, incorrect sensors, etc.
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Only issue is, I have family obligations in a little while and I can't get gross and sweaty in my garage today (not until this evening anyway!!). So, can anyone tell me for sure, where the BLUE pin is supposed to get its ground from? If I recall correctly from earlier in the thread, it's supposed to get its ground from the ECM, pins 1, 2, and 4. I've tested ground on those pins multiple times in the last week and they are definitely grounded. I suppose this could still be a logic issue if the ECM is supposed to toggle ground to those pins, but I suspect I have a bad connection in my fuse box, or I am just missing a ground somewhere (I've checked this a bunch of times ... good ground to engine strap, headlight harness ground, a ground to the engine block on the underside of the intake manifold behind the alternator).