trouble code reader

Does anyone know how I could make my own trouble code reader for my '91 Protege? I found schematics and instructions for an RX-7 (it basically consisted of an LED, resistor and some wire), but I think the Protege would be different. Or maybe the reader would be the same but where you connect it at would be different?

Thanks!

you cant do that to an obd 2 computer...all you need is to go to autozone or advance or whatever your local parts place is and they will read the code for free.

I thought the 91 was an OBD 1, was I mis-informed?