warning light. over heating!!!

["sharp"]

ok so im new to this whole supra thing. I bought a 86 non turbo a few days ago. i thought it looked like a pretty cool car. after I drove it i wanted it even more. i reasearched the car and everything checked out ok. I bought it and was headed home. after a while of driving I noticed the raideator light had come on. not sure when it came on but it was on. my temp was fine and stayed fine for a long time. after quite a while longer my temp had gone sky high. I pulled over and ran water over the raideator. I got it home let it cool but the light wont go off. it hasnt over heated again but i havent been doing any highway driving like i had been on the way home. i bought a new raideator cap but...no sucess. any ideas on what i should do??