1989 Ford Ranger Starter Wont disengage.?

Our 89 Ranger, 2.9L V6's starter one day decided to engage, start the truck, and not disengage. We yanked the battery cable to kill it so not to kill the flywheel. after some poking I just jumped the wires on the relay to start it, which means the starter will engage/disengage how it is supposed to, it is a power supply issue. So far we have replaced the: starter relay on the fender, and the ignition switch on the column. What is causing the starter to stay engaged when properly connected?