You probably won't be able to find a factory harness for a '93 auto but you can make one fairly easy.
You will need the NSS(neutral safety switch) and then a connector for it, they used the same NSS on Rangers from 1983 to 1994, and most Fords/Lincolns with automatics during those years, so wrecking yard may have connector that fits.
NSS has 4 pins, 2 are for starter relay, so starter motor can only be activated when transmission is in Park or Neutral.
And 2 are for the Reverse(backup) lights.
The reverse lights will be the easiest since the old manual trans Reverse light wires will be there next to the automatic
With NSS installed, Block the tires and shift trans into Reverse, now use an OHM meter and test all 4 pins to see which 2 are connected, 0 ohms, mark or remember them.
Shift trans back to Park, and test same 2 pins, they should now be disconnected, very high ohms or N/C(no connection).
Connect the 2 manual trans reverse wires to these 2 pins, 1 wire to 1 pin, other wire to other pin, order doesn't matter since this is just an open or closed switch.
When key is on 1 wire will have 12 volts, the other wire runs to reverse light bulbs, when trans is in reverse the switch is closed and the 12volts goes to the light bulbs.
Test the other 2 pins while you have the Ohm meter out, they should be 0 ohms(connected) when trans is in Park or Neutral, and high ohms or N/C, when in Reverse or Drive, these are to pass voltage to starter relay but only when trans is in Park or Neutral.
On a manual trans Ranger there is a Clutch safety switch located on the clutch pedal's push rod, there will be a Pink wire and a Red/blue stripe wire, you can simply connect these two wires together and starter motor will work no matter what position trans shifter is in, but I would splice longer wires to these 2 wires and run them to the 2 pins on the NSS, so starter will only work in Park or Neutral.