Hey Scotty! I have a 1989 Mercury Grand Marquis that the starter didn't disengage when I let go of the key. It just stayed engaged with the engine after it started. I immediately shut the engine off and the starter kept turning the engine for about 10 seconds. After this happened I pulled the negative battery cable off and then put it back on immediately. After this I could start the car and the starter disengaged normally. Ijust just replaced the battery that had tested bad. The only difference between the original battery and the replacement is that the replacement is the original was 690CCA and the replacement is 850CCA. The replacement is also slightly larger but AutoZone said it was compatible and it fits without issue. The engine turns over noticably faster with the starter sounding at a higher pitch than with the old battery, but I am thinking that this is because the old battery was weak/bad. Do you think this means the starter is failing? Or that it doesn't like the higher capacity battery? Or something else entirely?
replace the starter