codes for 1988 dodge d150

the check engine light is one and i have tried turning the key on and off is there a timed sequence or something i need to know to get the light to blink and when it does how do you read codes and what do they mean. I think the o2 may be out because i get very bad mileage and it smells rich but I don't want to spend the money to replace the sensor unless i know thats whats wrong