1991 Ranger will have an A4LD automatic
There is a Vacuum hose on the passenger side, check this hose for ATF, shouldn't be any of course, part is called Vacuum modulator, but doesn't read like your problem, just a good thing to check
It doesn't have a shift cable, it does have a 3-4shift solenoid inside the transmission, also a TCC(torque convert control) solenoid, locks torque converter when driving for better MPG
You can test both solenoids with an OHM meter from the outside of transmission
On the drivers side, just in front of the shifter, will be a 3 wire plug in, check that its there and plugged in
Example of plug in here:
https://www.ford-trucks.com/forums/attachment.php?attachmentid=63585&d=1351733124
The center wire gives both solenoids 12volts when key is on, so is connected to both, the other two wires connect to the computer, computer GROUNDS that wire to activate that solenoid
Unplug the connection
Test if center wire has 12volts, key on, if not its a wiring problem, no fuse for this one, 12v comes from PCM power relay, and engine wouldn't run if this relay or its fuse was blown
If you have 12v then turn key off and switch meter to OHMs
On the transmission side connector put one probe on the center tab, and the other probe on either other tab
you should see 26-40 OHMs, test both
If one is out of range then pan will need to come off to replace one or both solenoids, its not hard to do
If solenoids both test as OK and you have the 12volts, then its most likely a wiring issue from that connector to the computer behind passenger side kick panel in the cab
Computer pin 52 is for 3-4 shift, 53 is for TCC
And just as an FYI, above the shifter on drivers side of trans is the NSS(neutral safety switch), this tells computer when you are "in gear" but also passes starter activation voltage when trans is in Park or Neutral, AND also activates Reverse/Backup lights