The simple method for reading codes can be frustrating. There are initial codes, then the test codes, then closing codes. And they all have to be counted visually with the check engine light or an analog volt meter by counting pulses and pauses. At various times you need to perform functions based on timed intervals (like pushing the accelerator to the floor). It is a bit like trying to read Morse code but never having done it before. Some tests are done with the "
Key
On-
Engine
Off" and others "
Key
On-
Engine
Running."
There are code "readers" but they are not like OBD II. The simplest plugs into the test port and basically flashes a light like the CEL on the dash does and a switch to trigger the test. They also have a buzzer if you are more audibly inclined. You still have to do the interrupting of the pulses and pauses so it is not much of a help. These are in the $10 range on Ebay.
http://www.summitracing.com/parts/equ-3143 There is a somewhat more expensive type that as far as I can tell does the counting for you and displays a code number. I actually have one, but have never used it. These are in the $30 range. UPDATE: I just tested mine. It sure takes the "Mystery" out of counting light flashes and pause counts. It does display an actual number! This comes with a book that delves into the deeper side of OBD I too.
http://www.summitracing.com/parts/ino-3145 Ford also had a dealer style Rotunda reader and I think it piggybacked on the ECU. These are not cheap and if I recall correctly when you find one (the right one) are easily in the $500+ range.
Lastly be very weary of any reader that "says" it is OBD I and has even a hint of being an OBD II reader. From what I saw these would never work. Innova and Equus are the only two "real" OBD I (Ford) readers I am aware of.
You will have had to retain or reinstall the test port from the ECU. It is a somewhat triangular connector with a single wire connector associated with it. There is all kinds of stuff on the internet about OBD I (Ford) but you might try The Ranger Station
http://www.therangerstation.com/ or NATO
http://www.turbotbird.com/ as they deal with swap issues. Be careful too because I have seen where not every OBD I (Ford) code number is the same for each engine. Be sure the codes are specific to your engine/year.