Ill use my code reader, I just hate the flash flash bullshit but it does work.Do the old paperclip trick for OBD1 (Pre 1996) and look up the code.
Pulling the computer codes:
Under the dash by the driver's left knee you'll see a connector with two rows of pins. That is the ALDL (Assembly Line Diagnostic Link) connector. Pin A is in the upper right-hand corner (as you're looking at it), Pin B is right beside it.
Bend a paper clip or small piece of wire into a U shape and insert it into both pins A and B so that they are connected together.
Turn the ignition switch to the ON position, but don't start the truck.
You'll see the "Check Engine" (or "Service Engine Soon" on some models) light flash some codes.
Error codes are two digits, and the light flashes out the first digit, pauses, and then the second digit. It will repeat each code two more times (total of three) before displaying the next one. The first and last code will always be a code 12 (flash, pause, flash, flash, long pause, repeat). This code is normal and means that no tach signals are making it to the computer (because the engine isn't started). If you don't get a code 12, something is wrong with your jumper or your computer.
Make a note of any codes that come up! Code 12 will flash 3 times in a row, then whatever has tripped your CEL will flash. Google for it or post it up!