Good stuff. I did read that previously, but when remote troubleshooting sometimes we have
to restate the obvious just to make sure that we are still on the same troubleshooting page.
The Factory Service Manuals are the best documentation we have to work with, and
while I consider them to be very good, they are not an absolute reference. Actually,
oftentimes the very best reference out there is descriptive text and photos from fellow
GMT400 members. (Discovering this is what attracted me to joining this forum in the first place.)
That ground strap is a perfect example of what I'm trying to describe. To further this conversation, I took the
liberty of adding an arrow to Caman96's photo that points out his woven ground strap in the lower foreground:
You must be registered for see images attach
(credit:
@Caman96 in Big 3 discussion elsewhere in this forum.)
FWIW, Caman96 has a really nice truck, and everything is pretty meticulous, so if his ground
strap routing doesn't match the factory drawings it's because he found a neater/cleaner way
to route it. :0)
By the way, if this ground strap is MIA on your 26 year old truck, that's quite possible. If it
was missing before and the truck still ran, then the powerplant must have found an undocumented
ground elsewhere, maybe through something like a worn motor mount? Or possibly the ground strap
was relocated by the PO? For more info on all this, just search the forum for "The Big 3", and there's
plenty of discussion about the these high current capable electrical cables.
To be perfectly candid, I've been puzzling over this. You made an earlier comment about retrieving
the ICM from the donor vehicle. Since you actually heard this combo run before you acquired the motor,
I think that this is a prudent idea, and covers an important variable.
And also keep in mind if my failure theory is correct (ie: excessive voltage in Coil secondary due to working
into an open circuit causing arcing/shorting back into the coil primary windings > ICM) ...then this means
that the Coil is also suspect. Maybe only wounded, but leads to the classic intermittent coil failure: works fine
at idle in the driveway at lower spark voltages, but fails when the pressure is on and spark voltage rises in response?
****
To cut through all the mumbo-jumbo, at this point I would focus on just getting your electrical system as close
as you can to what's in the Factory Service Manual. And the fact that the behavior of the truck has changed
(from lights returning 3-5 minutes after attempted cranking to lights never return?) is something we need to
really understand before continuing. When the electrical system is healthy and wired in accordance with the
factory wiring diagrams, I should be able to crank over the engine and at the same time not adversely affect
any other circuit? Or even if I do have something go wrong in the cranking circuit, it should
still not affect
the dashlights/headlights?
So let's take a hard look at the electrical system in this truck, get any blown fuses documented/replaced,
headlights back on, ground strap (Big 3) identified/verified...and at some point we will be at the point where
we are going to attempt to crank the engine over with the starter (and spark plugs still out) and be able to
do so without causing any headlight misbehavior.
Who knows? We may discover that in all the excitement a couple of logically-unrelated wires got smashed
together during the engine swap, and finally all this will make sense. (As one of the few wrench-turners in the
neighborhood who would admit to knowing anything about electricity in public, I was always invited to post engine
swap parties like this back in the day. Never fun at the time, but the beers always tasted that much better once
we figured it out and the machine was making noise again. :0)
Hope this helps. Let us know what you discover, for that is what will make this thread truly valuable to
the community.
Cheers --
