How do you check OBD on 1991 Mazda 929 s?

To check the OBD on a 1991 Mazda 929, you'll need to locate the diagnostic connector, which is typically found under the dashboard near the driver's side. Use a jumper wire to connect terminals 1 and 2 on the connector to put the car into diagnostic mode. Turn the ignition key to the "on" position (without starting the engine), and the check engine light will flash to indicate any trouble codes stored in the system. Count the flashes to interpret the codes, which can then be cross-referenced with a service manual for further diagnosis.