If anyone can comment and help that'd be awesome! 1996 GMC Yukon 5.7 V8 4x4, 4-door Automatic.
Crank but won't fire condition with no spark (now, sputtered before and wouldn't start).
Troubles began when engine didn't turn off when the key was turned off. Engine ran fine when it ran.
Disconnected battery.. stayed running... disconnected fuel pump relay then it finally shut off. A real pain when you have errands to run!
***Dash Batty light and brake light stay lit when ignition is off***
Have a current drain going on when the engine (and key) are off. (I disconnect Batty and keep it charged)
Replaced the ignition switch (had to, it fried in my hands, tried to fry my truck, definitely something going bad there).
Dash batty light and brake light STILL lit when ignition is off.
Replaced the ICM. Tested old compared to new, new had 1.92 ohms resistance between pins 1 and 3, old was open. (Body of ICM was towards me when testing, don't know which was left or right or proper pin #, that was the only resistance reading I got)
I don't have an oscilloscope unfortunately, just digital multimeter.
Dash batty light and brake light STILL lit when ignition is off.
Tonight tested spark plug, no spark.
Tested high voltage out of coil... nothing (I removed high voltage lead, inserted 1/4 drive extension into HV socket, made contact, connected to jumper cable, and said cable to spark plug tip, grounded the other end... no spark) farmer-tizing it but that'* all I could think of.
No issues with alternator, when it ran it charged fine. Possible issue?
The other strange thing is after it'* sat for a bit and I turn the key to RUN and I can hear the fuel pump whirrr. But then immediate subsequent attempts I cannot hear the pump. (I replaced fuel pump this summer) However, I have fuel pressure at the rail, not sure what the pressure is because I don't have a fuel pressure tester (yet).
Any suggestions would be welcome. Even asinine comments at this point LOL. I am so frustrated with this cf I'm about ready to torch it. Give the local fire department some practice.

Maybe a question or two. I can't follow your map.

Mainly now the issue is it cranks, won't start or fire, no spark. When ignition is off I still have dash lights on: Battery and Brake.

I would look at the fuse box and see if you have corrosion>Look at the underside and at the pins.
Any codes?

Will do. No codes.

Most likely area for a bleed through is the fuse block.
I'd look at the under hood one first. Use a good light and any green corrosion is suspect.

Pulled fuse block in engine compartment. Didn't find an issue. Cleaned contacts on all fuses and sprayed the inserts with electrical cleaner.
Since the dash Batty and brake lights were still on when ignition was off, I started pulling fuses and relays and connectors.
Pulled and reinserted the 10A gauges fuse on the inside fuse panel and now the dash lights stay off when ignition in off., Kind of good news.
Now have no spark.
I have 12V at the coil and ICM connectors.
I'll recheck ohms on the new ICM to see if it has changed.

I have the service literature if you need something.

Thank you. Do you know what the rectangular component is on the manifold right behind the throttle body? I cant find anything yet on the internet.

My logic is that if I pull connectors, I may find a system that is causing the issue which might help narrow down the possibilities.
I think the battery drain was coming from the current pull on the lit dash lights which reset after I pulled the fuse.

What would be the best manual to get? I'm only familiar with Chilton and Haynes.

What resistance range is normal for secondary winding on ignition coil?