1973 Chevy Truck starter keeps running

Electrical problem
1973 Chevy Truck V8 Two Wheel Drive Automatic

truck would not shut off when shutting key off, replaced key switch then when starting truck starter would not stop running, found lead to selenoid melted in half at exhaust manifold replaced wire still starter would not stop running, replaced ignition swith and key switch still keeps running, checked selenoid and it is good, now when I remove the battery lead and then reinstall battery lead everything ok until I try to start the truck then the starter keeps running have to remove battery lead to stop it.