The overdrive light will be off when the overdrive switch is pushed in. If the light flashes then that's a trouble shooting code.
Overdrive switch is located on the gear shift stick, just below the handle. You could toggle with your right thumb to see if the O/D light comes on when pressed.
Take it in. There is either a problem with your transmission or with the overdrive switch itself. Overdrive switch should be a lot cheaper to fix. I'm assuming the light not only goes on, but the overdrive physically turns off as well when the light is on.
I have a 1996 Prizm LSI and the OD switch is a small round button on the side of the shift lever. You could have accidentally switched it off and that is why you get the light.
You will have to remove the instrument cluster. This may be an LED that should never have failed.
There is no separate switch for it. Pushing the light switch will defeat the dome and courtesy lamps.
Usually on the dash to the right of the steering wheel.
On the brake pedal assembly.
Chances are that the overdrive solenoid (forgive my spelling) inside the transmission needs replaced. Not a job for the light-hearted.
Overdrive on is the normally allowed position , if the overdrive switch is pushed that is located on the end of the gearshift lever the word OFF is supposed to light up
On the upper dash right of the steering wheel next to the overdrive (OD) switch
Overdrive ( basically the 4th gear in your 4 speed automatic transmission ) It allows you to drive on the highway / freeway with the engine running at lower RPM's . The engine is quieter and will get better gas mileage The O/D OFF light will come on in your dash if the switch on the end of your gear selector lever is pushed . Pushing the switch again will allow the overdrive to be used , as will shutting off the vehicle and the next time it is started the overdrive is allowed which is the normal position