How can i fix my speedometer (toyota lucida estima model 1993)?

I own a toyota lucida estima van, diesel, automatic transmission and 1993 model. My speedometer is not working and i have noticed then that that is the beginning when my overdrive indicator in the panel lits on and off when i supposedly reaching the 4th gear and stays as is even when I am now in park shift position. I have to shut off the engine to eliminate it. What are the problems? Your help is being appreciated. thanks.