Well, I just got it started.
I do not have a kill-switch installed yet (It's in the master plan) but as part of this drivetrain re-installation I did install the Battery Cut-Off with Fuse. I had previously removed it to eliminate it from the equation but re-installed it after the car started. This go-around I just left it on as I was getting a good ground and reading from it.
I still don't know what the issue is and I imagine it is going to leave me stranded somewhere until I can definitively identify what is causing this random no-start issue.
Here is what I did since my last post:
1st Attempt:
Tested trigger-wire again for voltage.
Passed
Charged the battery to 100%
Jumpered solenoid + to trigger post (removed yellow trigger wire first) - Starter kicked in -
Passed
Tested that the starter is grounded:
Used multimeter from:
Solenoid to transaxle ground - Passed
Solenoid to transaxle body - Passed
Solenoid to starter body - Passed
Attempted to start -
Failed
2nd Attempt:
Connected jumper cable to negative battery post and starter mounting bolt in engine bay.
Attempted to restart while wiggling key - Initially failed for a split second but then started. -
Passed
I disconnected the jumper cable and tried again several times -
Passed
I tested it again with the headlights on. They turn off when I turn the ignition to start and until the motor starts. Is this normal behavior? I believe it has always worked this way on my car.
So I am still stumped. I don't know why wiggling the key would work since the solenoid was getting 12+ volts at the trigger, the positive post was getting 12+ volts continuously, and the starter proved to be well grounded.
It is starting better now than ever but I know it's just a matter of time before it leaves me stranded as I really did not determine why it was failing. Perhaps I will pull the ignition switch to investigate further.
I was hoping it wouldn't start until I found something obvious.
Thank you everyone for the feedback.