UPDATE:
Good News Guys - She's Running!
Excellent! Sincere thanks for staying with this and working it logically all the way through
to the successful conclusion. And by sharing what finally fixed your electrical anomaly, this
changes the thread from just FSM-based theory into a real-world troubleshooting process
and a specific fix that others can learn from.
And, as most of you have already experienced in your years of wrenching, it was a stupid little thing. The Battery's Negative Terminal Bolt.
...Once I isolated the system and essentially bypassed only the Negative Terminal Bolt, I knew that had to be the problem.
I installed a new one, plugged everything back in and she fired up first turn! Can't believe it - $8 and weeks of time!
I was happy to read your synopsis above, for this was my stated goal back towards the beginning:
But my goal for sharing all this is for you to be able to troubleshoot to the root cause in as few moves as possible. And more importantly,
once you fix this you will understand exactly why it failed in the first place.
At about the halfway point, we had so many questions that it was near impossible to
come up with a good theory as to why. When there are too many unknowns/variables,
this is when we go from a big picture/top down troubleshooting approach, to a bottom up
Building Block strategy:
No doubt you are aware that we are dealing with something out of the ordinary. Doesn't mean that it can't be fixed,
but it does mean that we are going to have to assume everything is bad, and go through the effort of proving to
ourselves that each piece of the powerplant puzzle is good.
Which you did. Without firing the parts cannon. (aka: Ready, Fire, Aim. :0)
There are probably some who are reading this exchange who are thinking, just replace all the stuff with new and move on. I’m getting there myself, but I really want to know the specific reason this isn’t working so I’m better equipped in the future.
Congratulations on achieving your goal. I'm sure that you feel a lot more comfortable now
with the GMT400 electrical subsystem than you did prior to starting this engine swap. And
I also hope that your son enjoyed learning how Analytic Troubleshooting / Symptom Directed
Diagnosis is used to tighten up the problem description and help develop a structured testing
approach.
Thank you for all of your awesome help! This forum has to be the BEST I've found!
There are a *lot* of good, sharp, helpful folks in here. It's one thing to drive something
old solo. Quite another to drive old with all the documented info and years of experience
here in the GMT400 forum to tap into if necessary. A lot less stress & way more fun to boot,
especially given the feel/vibe of those who choose to be a part of the old truck community.
Now that you've regained control over the electrical system, best of luck with the remaining
loose ends of getting your truck back to work & earning it's keep.
Safe travels --