No codes, "Service Engine Soon" light stays on steady, no flashing

Joe, can't thank you enough for going to such lengths. Thank you!

Please let me clarify what I need to do:

All of these checks to be done with the key in the "on" position:
1. Pic #1 - check for 12 volt in the black/white wire of the right hand plug in the ECM (which I'm assuming is all the inputs)?
2. Pic #2 - check for 12 volts on the pink/black wire in the plug on the left of the ECM (which I'm assuming is all the outputs)?
3. Pic #3 - this looks like a connector located on top of the steering column under the dash, which should have two plugs. I am to check the one closest to the steering wheel for power - somewhere in one of the leads?
4. Pic #4 - find the connector behind the glove box coming out of the wire loom from under the heater blower and check to see if 12 volts are present?
5. Pic #5 - is this the fuse block behind the cover on the dash under, and to the left of the steering column? If so, check the 10am fuse at Position #177 and #178?

If all my assumptions are correct, you do not need to reply. Please correct me if I am assuming incorrectly. I will do this in the AM and report back.

I have a question - I see 4 screws that appear to hold the instrument cluster into position. If I remove those 4 corner screws, is it possible to pull the instrument cluster forward and examine the back side of it? I'm wondering if someone has messed with that and disturbed the wiring.

Again, thank you very much!
Rich

Joe, please let me tell you "the rest of the story". I met a guy who convinced me his specialty was tracking down oddball issues like this one. I took a chance since the cost was not too much. We discovered some prior owner had installed a "performance chip" that was inserted between the ECM board and the OEM eProm via a 90 degree connector. This guy tested the ECM traces down and found 5v on the trace leading up to the white/black wire but no signal coming out. Neither of us had ever seen a Performance Chip and had no idea it was anything but OEM. After some research, we discovered that part was aftermarket. Once it was taken out of the circuit, the truck ran fine and the OBDI port acted normally. Odd thing happened to me on the test drive - the truck stalled while driving about 35MPH. I had purchased a remanufactured ECM that had been installed. After several tests, we discovered the board had a minor crack in one of the traces and when the truck hit a bump, power was lost (engine stopped). Once we discovered this, we put back in the OEM ECM and the truck has run great ever since. This was a odd case and I apologize for putting you through hoops that was not needed. I'm sorry. My only defense is not knowing what a Performance Chip is or what it looked like. I am in awe of the truck, it runs great. Now I just have to get the A/C fixed. :-)
My very best,
Rich