Why is my over drive light on and wont work on my 93 ford probe?

I bought a 93 ford probe and the o.d. light is on and flashing on and off all the time, It don't work and my car is getting bad gas mileage! anybody know why and what could be the problem?|||I had the same problem. Unfortunately, you`re going to have to get used to no o/d. I never got mine fixed, but I was told it was a sign of a needed rebuild.|||It could be either the transmission itself, or some kind of overdrive module, or sensor. I'm not a big Ford man, so sorry that's all I got for you! Good luck.