Starter Problems

I was having problems starting my 1993 f150. So, I changed the starter the battery cables and the solenoid. After going through all the possible fixes for this problem i'm still having 1. If I hold the key foward to crank the truck the starter stays engaged, but if I just tap the ignition and let the truck start itself the starter will disengage but the battery light will come on and the battery will drain. Has anyone heard of this problem and if so could you help me out. THANX.

Maybe an ignition switch.