So, now that it's running, I figured that I would put down what I learned and how I tested it all.
As I have been thinking about this tonight I realized that when the gear indicator moved through the drive gears, it showed where the range selector switch wasn't working. So how does the range selector switch signal what gear you have selected? I was stumped since there are only four wires signalling six different positions, until I really got the wood burning. The switch controls grounds for the PCM, and depending on what combination of grounds, the PCM sees what gear you have selected.
Pin 7 is grounded in N, D and L
Pin 8 is grounded in P, 3 and L
Pin 9 is grounded in P, R, N and L
Pin 10 is grounded in P and N
Put another way:
In P, pins 8, 9, and 10 are grounded
in R, pin 9
in N, pins 7, 9 and 10
in D, pin 7
in 3, pin 8
in L, pins 7, 8 and 9
Now that I have this typed out, I can see that pin 10 circuit must not have been working. Actually, this gives me more confidence that the switch was the problem and I just needed to reset everything.
The range switch was about $50 so it's not expensive, but you need to ball-up to swap it out since you have to drop the trans oil pan and valve body:
Start by disconnecting the shift linkage. It just pulls straight up. Then loosen the bolt on the shift lever where it attaches to the shaft going into the transmission.
Have a drain pan handy and drop the transmission oil pan and filter. Find the 10 MM-headed hex bolts; there are a bunch of them, I didn't count. When you get the last ones out you will get more oil running out so be ready. The valve body will now drop out. The shift shaft comes out with it so you have to wiggle things around a bit to get it to come down.
CAREFUL. This is where the pucker factor increases. There are two accumulator pistons with springs that are held up by the valve body and they WILL fall down when you lower the valve body. I wasn't ready for this so I had to spend some time figuring out what went where since one piston had two springs and one had one spring. What it came down to is that... you know how that grey metal dirt coats stuff in a transmission? I saw where the springs sat on the plate of the valve body and I saw the witness marks of the inner spring in one spot and not the other.
Anyway, you should now have the valve body in a clean work place. Just one torx-headed screw holds the switch in place. Remove it and the switch comes up. There is a seal on the shift shaft and in a perfect world, you would want to replace that seal after you put the new switch in place.
To install the valve body with the accumulator pistons and springs, I cleaned the parts and the bores with brake cleaner and blew them off so they would be dry. I then loded things up with Vaseline brand, pure petroleum jelly and put the accumulators and springs in the bores. I forgot what the torque is on the bolts. Sorry.
Other than that, assembly is the reverse of removal.
The grounds for the PCM run through the four pin connector near the PCM in front of the front, left wheel. It's the black wires, I didn't get the pin numbers. They connect to the battery ground. To test the circuit, I pulled the connector from the PCM and found pins 13 and 14 and - with the four pin connector connected, I used a test light. the clip was one the battery positive and I probed pins 13 and 14 with the pointy end. Since the test light lit up, that showed that the ground was good. I could have used a multimeter to test resistance, but with the test light, that puts a load on the ground circuit so if there is corrosion or something in the circuit, this will show it. A nice, bright light is a good thing - a dim light indicates high resistance.
I'm tired now and maybe I'll think of more information later.