starter prob

i just put a new starter in my 95 z28. now when i turn the key to start, which is right after the accessory position on the ignition switch, the starter cranks all the way by itself. the engine starts running and the starter doesnt disengage and it keeps cranking. ive asked around and some techs (without looking at it) have told me i have my wires crossed which is impossible because there are only 2 wires and they are different sizes. my uncle says its the switch at the bottom of the steering column. whats going on here?
thanks
-jose

Could be the gears binding up so the starter gear can't retract to get out of the flywheels way when it starts running.