I have a 1988 FORD BRONCO, full size, that has a peculiar problem. I tried starting the car and it turned over, but when I tried shutting it off it kept turning over. I had to disconnect the battery to stop it. I replaced the solenoid being careful to route the wiring connections the same way. I tried starting it and it shut off using the key switch the first time, but when I tried starting it again it wouldn’t shut off so I had to disconnect the battery. Any suggestions on what might be the problem? The ignition switch??
It could be the ignition switch or the starter bendix could be stuck in the flywheel or flex plate if the transmission is an automatic. You will need to remove the starter and inspect it carefully. Inspect the flywheel or flex plate gear teeth as well.
The solenoid mounted near the battery is the most common cause for that problem on older Fords and it is cheap and easily replaced.
Try it again, but this time be ready to disconnect first the wire on the solenoid from the ignition switch, and if that doesn’t stop it, then the power wire from the battery. This will tell you if the new solenoid is faulty (not unheard of).