1987 supra heater/defroster controlls

Thankyou for your responses. No I didnt get a manual with the car.
The radiator is topped off and the light runs steadily, I, also not too long ago, changed the anti-freeze. The last time the light flickered intermittently the thermostat was bad. So I am not sure what this is about. About the time I started getting the light again I did have problems with the overflow. The water was not going back into the radiator from the reservoir after it cooled down. So I cyphoned out the water in the reservoir and started over. Since then I do not see that it is going into the reservoir but then again I forget to check when its hot, so it might be working now. But the light remains.
Thankyou for your help
Roxanne