I have read tons of posts seeking answers to these questions and now, with eyes afire from reading, I ask:

1) The "gear range selector window" says, "P, R, N, D, 2, 1" . Is there any way to go into (as in, 'hold it in') 3rd? I'm thinking it could be helpful descending hills as it's more a driving gear than a start-up gear. I know OD OFF will limit it to 4th at speed.

2) My 4WL works fine. Why did Ford require the trannie to be in N and not P? Isn't P effectively neutral? My guess there is that the NSS itself must be closed and it is not when in P.
Also, what signal does the depressed brake pedal (also necessary) send and to what?

3) A thread on a 1998 Ranger described P1705 and P1501 as test codes. Is there any info those codes provide and does this apply only to 1998-2000 vehicles?

This is what happens when you're slightly laid up with a bad hip bone.

 

For #1, no, those selections are all the 5R55E shifter inside the transmission has, this transmission was a C3(3 speed) to start with(1974), so 1 2 and D, then OD was added making it an A4LD but still 1, 2, and D, D had a circle around it for OD
And some had the 1 and D and then OD, but no 2 in that case, OD, D, 1

4R and 5R just had more solenoids and newer software in the case of the 5R
Inside the trans on the shift rod are the available selections, seen here: https://i.ebayimg.com/images/g/M8QAA...4fg/s-l400.jpg
There are 6 "detents" that hold the trans in the selected position
P R N D 2 1 = 6 positions
So no 3 without a major redesign..............BUT, put shifter in 2 and start driving, 5R has a faux 2nd gear(1st + OD on), see if you get 2 shifts, if so then 2 is actually 3

#2, it used to work in P or N but Ford changed that, I think with the 1995 change to the 4R55Es, the older A4LD had a simpler NSS(neutral switch) above the shifter, Park and Neutral both closed/connected the same 2 wires so no separate P and N
The 4R got the DTR(digital transmission switch), on the shift rod and had more contacts and so P and N were different contact closures, so N could be used on its own

The brake pedal switch is actually 2 switches in one box, it has brake light switch(12volt) and a brake pedal sensor(5volt or ground)
What does what changed over the years, the 12volt activated the brake lights, of course, and could also disable cruise control if it was on, in some years it also activated the shifter interlock, so you could shift out of Park
Sensor can show foot off the pedal or on the pedal more reliably since it has 2 readable positions, 5v or ground, 12v switch just has 12v or no volts which could be a burnt out fuse not foot off the pedal
So sensor is used for cruise, 4l, ABS and I am sure other things I can't think of right now, lol

#3
P1501 Vehicle Speed Sensor Out Of Self Test Range
Could be VSS/OSS issue, depends on the year, but it means that the "speed" signal sensor is disconnected/failed or its signal was out of expected "range"
Speed sensors are Variable Reluctance(VR) type, this means they generate their own AC voltage from being next to a spinning metal ring with "teeth" each tooth cause an AC voltage spike, the voltage is not used the sine wave pulses are the speed signal
VSS, OSS, ABS, Crank and Cam sensors are all VR type
So the code could indicate erratic pulse or no pulse at slow speed or no connection to sensor

P1705 Tran Range Circuit Not Indicating P/N in Self test
Means what it says, When you turn the key on in an automatic computer expects to see DTR showing Park or Neutral if starting engine, and it didn't see that
Could be loose column shifter, a common issue on Ford Trucks in general, so trans its shifting in to Park but not moving shifter far enough for DTR to show being in Park

 

Got it. The planetary lands on a stationary coupling. Brakes make it OK to actuate. I just looked at a picture. Duhhhh Thanks