1988 Ford Van E250 5.8 liter engine
starter pinion doesn’t disengage
starter keeps going with key off until battery is disconnected
Follow the positive battery cable to the starter relay. Remove the wire with the rubber boot from the relay. It just pulls off.
Now reconnect the battery and if it no longer cranks look for a cross in the wiring between the ignition switch & relay or a short in the ignition switch.
The wire should have 12 volts on it only when the key is turned to the start position.