Found a video about testing the PCM to see if it breaks the ground to shift the transmission. From what I could gather I believe it works this way: The power is supplied to the solenoid from the EEC power relay. The ground is supplied by the PCM. At the correct shift point (mine has always been about 45 mph in 3rd gear historically) the PCM drops the ground and the solenoid makes the shift to overdrive. Well, I tried this out with my DMM connected to the tan/lightt blue wire and a good ground in the cab. key on gave battery voltage (12.6V) and once started had alternator voltage (14.3V). at shift point voltage dropped away to .352V. surprisingly though, it would not come back to battery voltage even after stopping. Decided to crawl under the truck and look at things. You probably have an idea what I found. The split loom for the wire harness to the solenoids was laying across the back of the exhuast manifold and the crossover pipe. The loom material was fried. The wires within got hot enough for the insulation to all melt together. I am going to pull the harness out tomorrow and go about separating the wires and inspecting for any problems which I am pretty sure I will find. My question is this: Is it possible that a short in one or more of these wires could have also been the cause of my computers failing? Also, is it posssible for me to test that the solenoids are working and not stuck by providing power to the red terminal and ground to the other two manually? Wires are not the same colors as what you gave, RonD. Not faulting you by any means, just saying I found them to be white and Tan/light blue. later found this diagram on the internet.

 

Good find, but what a pain

Yes, all the solenoids get 12v with key on
The computer has the ground for each solenoid and it "looks" for 12v on each ground wire with key on to make sure the solenoid is connected
Surprised you didn't get transmission codes if bare wires were shorting or grounding

Yes, these ground wires should show Vehicle voltage(engine on 13.5v+), until computer uses that solenoid, so grounds it, then voltage would drop low on that wire

 

Well, it was very ugly and not the easiest place to work in but I got all the wires spliced, ran continuity checks on each of them, and got the harness secured away from the exhaust. Put in a new computer and EDIS module at the same time. I took it out for a shakedown (about 45 miles of all different types of driving) and no CEL. Got an added bonus as the fuse for the turn signals/backup lights is no longer blowing. I guess one the wires from the trnasmission is on that circuit for the backup lights. Anyway, got home and looked for codes, still giving code 16 but no others and the CEL doesn't come on. I have replaced everything on the ignition system now and can't figure out what would be causing that code. It doesn't seem to be affecting anything though. Again I want you to know just how much you have helped this old man out RonD. I couldn't have gotten this done without your help.

 

Good work, not an easy job

16 is a Key on ignition fault code for V6 engine, not an engine running code
So its odd its still there

 

Yeah, And I have no idea what could be causing it. Truck seems to run fine, better than ever actually. hits all the shift point, accelerates very well both gradually and quickly. I haven't torn the steering columne apart to check the ignition switch itself but it seems to work just fine. The barrel lock is totally worn out but I like it that way. I never use the key anymore so they stay in my pocket and I'm never locked out by leaving my keys in the truck now. I guess I will just have to wait and see if it gives me any greif.