OBD 1 gave quite a lot of information but it wasn't readable on a computer screen.
It communicated with rudimentary Morse Code by flashing the Check Engine light on the dash a certain number of times with long and short pauses in between the flashes.
After you performed the requisite task to get the codes (flipping the key on and off a certain number of times (Dodge), jumping a wire under the hood with a paper clip and then revving the engine and turning the wheel lock to lock (Ford)) you would count the number of flashes and pauses and write them down.
Look up the numbers in a manual and see what they meant. There were dozens of different diagnostic codes.
