You can actually read the OBD 1 codes (1995 and older) with nothing more than a paper clip. If you short the self test input wire to pin #2 on the diagnostic port, the CEL will flash the codes via. light sequence. Go buy a Haynes manual for about $17 and it shows you how and what the codes are.
Two caveats, some of the earlier OBD 1 computers won't show codes on the CEL, you actually need to use an analog multimeter to read them, and you can't read Fast codes without a scanner.