Welcome to TRS
You can get the code(s) by installing a jumper wire on the OBD1 connector in the engine bay and then counting the flashes of the CEL in the cab when you turn on the key
You will need to find the OBD Connector in engine bay, in 1989 its probably on passenger side between fuse box and firewall on the wiring harness
Video here: for what to look for: youtube.com/watch?v=RVbDHOiuKpQ
1989 Ranger will use 2 digit codes NOT 3
2 digit Code list is here:
https://therangerstation.com/tech_library/2digitcodes.shtml
There are no 0's just 1 to 9
Written version here of the video on how to connect jumper and also how to read codes with test light or volt meter:
https://therangerstation.com/tech_library/OBD_I.shtml
If you turn the key off while codes are repeating it will clear them, if you pull out the jumper wire while codes are flashing it won't clear them, your choice
Each code can have different meanings depending on the engine and computer being used
OBD(on board diagnostics) in this case, was developed to be used by Ford techs not DIY mechanics
And the same applies to this day, code definitions are not in "english", lol, they are close but meaning is not always what you may think
i.e. Lean code does NOT MEAN engine is running Lean, it means computers calculations are off, low, so possible vacuum leak