Test Q: Overdrive (O/D) Off Indicator Inoperative

1. Test drive vehicle and verify O/D operation. If O/D operates properly, go to next step. If O/D does not operate properly, see appropriate ELECTRONIC CONTROLS article in AUTOMATIC TRANSMISSIONS.
2. Turn ignition switch to LOCK position. Install 104-Pin Breakout Box (49-UN01-130) to PCM following manufacturer's instructions. Turn ignition switch to RUN position. Using a jumper wire, connect terminals No. 24 and 79 at breakout box. Cycle headlight switch off and back on. If O/D off indicator illuminates, see appropriate ELECTRONIC CONTROLS article in AUTOMATIC TRANSMISSIONS. If O/D off indicator does not illuminate with headlight switch in ON or OFF position, go to step  5. If O/D off indicator does not illuminate with headlight switch in OFF position, go to step  4. If O/D off indicator does not illuminate with headlight switch in ON position, go to next step.
3. Turn ignition switch to LOCK position. Disconnect headlight switch harness connector. Turn ignition switch to RUN position. Rotate headlight switch dimmer wheel to full bright position. Measure voltage at terminal No. 9 (Light Blue/Red wire) at headlight switch harness connector. See Fig 1. If voltage is greater than 10 volts, replace headlight switch. If voltage is 10 volts or less, repair open in Light Blue/Red wire between headlight switch connector and fuse No. 11.
4. Turn ignition switch to LOCK position. Disconnect headlight switch harness connector. Turn ignition switch to RUN position. Measure voltage at terminal No. 4 (Red/Yellow wire) at headlight switch harness connector. See Fig 1. If voltage is greater than 10 volts, replace headlight switch. If voltage is 10 volts or less, repair open in Red/Yellow wire between headlight switch connector and instrument cluster dimming module.
5. Turn ignition switch to LOCK position. Disconnect headlight switch harness connector. Turn ignition switch to RUN position. Measure voltage at terminal No. 4 (Red/Yellow wire) at headlight switch harness connector. If voltage is greater than 10 volts, reconnect headlight switch and go to next step. If voltage is 10 volts or less, repair open in Red/Yellow wire between headlight switch connector and instrument cluster dimming module.
6. Turn ignition switch to LOCK position. Disconnect instrument cluster 16-pin harness connector C-214. Measure voltage at terminal No. 5 (Orange/Black wire) at instrument cluster harness connector C-214. See Figure. If voltage is greater than 10 volts, go to step  8. If voltage is 10 volts or less, go to next step.
7. Turn ignition switch to LOCK position. Disconnect headlight switch harness connector. Measure resistance of Orange/Black wire between terminal No. 5 at instrument cluster harness connector C-214 and terminal No. 8 at headlight switch harness connector. See Figure and Fig 1 . If resistance is 5 ohms or less, replace headlight switch. If resistance is greater than 5 ohms, repair open Orange/Black wire.
8. Disconnect Powertrain Control Module (PCM) harness connector. Install 104-pin breakout box following manufacturer's instructions. Measure resistance between terminal No. 1 (White/Light Green wire) at instrument cluster harness connector C-214 and terminal No. 79 at breakout box. See Figure. If resistance is 5 ohms or less, replace instrument cluster printed circuit. If resistance is greater than 5 ohms, repair open White/Light Green wire.

Fig 1: Identifying Headlight Switch Connector Terminals

Courtesy of MAZDA MOTORS CORP.