What to do when running lights on a 95 ford probe are on while this switch isn't on?

i recently put a stereo system in my 95 ford probe. I noticed a spark from the illumination wire on the wiring harness behind the radio, this is when the lights began to stay on. I figured it melted the wire to a constant power wire somewhere in the harness, I was right after pulling the wires away from one another hoping this wouldfix the problem...it didnt. what could be the best solution to fixing this situation. Thanks