Hello, I am trying to diagnose a "Crank's but will not start" problem on a 99 Yukon Denali.
The problem started when I got in and it fired up instantly. It was night time, and I noticed that there were no tail lights or dash lights illuminating. So I turned this...


And the tail lights and dash lights illuminated.

I cycled the switch through both settings, used the dome override switch, then turned the switch back to the "Off" position, and the engine IMMEDIATELY died.
After that moment, the engine only cranks over but refuses to start. (Does not even try to fire.)

I pressure tested the fuel system, and it show's about 62 psi when I first turn on the key, then it drops to about 58 psi. When I turn they key off, the system pressurizes back up to about 62.
I also tried some starting fluid and still no attempt to fire.

Am I looking at a possible ICM failure? BCM failure? VCM failure? DRL failure? Security system failure?

The way this thing shut off when I switched the headlamps off was like I had just switched the key itself off.

I'm very new to this vehicle and not quite sure where to start. (I bought it, drove it about 16 miles, parked it and this happened when I restarted it.) Any help is appreciated, and I will make sure and share the ultimate solution with other users, even If I end up having to take it into a service center.

The security light isn't flashing, but I do notice that the fuel gauge jumps then slightly "Twitches" or "Vibrates when the ignition is turned on.

Thanks for any suggestions as to where to start.

Edit: Worth mention that we had about 8" of rain here right before problem started.

 

Ok, good news! I found the problem today.

The High tension wire from the coil to the cap was grounding out.

Re-routed it, and it fired instantly.