Somebody help me here. I am not a mechanic, but i am fairly intelligent and very good with tools.

1988 F350 7.3 diesel with 130K
Great truck, havent had any problems since i got it in the spring.

The other day i went to start the truck, turned it over and it didnt start on the first try.
(this happens from time to time, but it always goes on the second try)

Well when i backed off the key, the truck continued to turn over. I repeated the motion on the ignition cylinder, took the key out, still turning over the engine by itself until it killed both batteries.

I replaced the starter solenoid thinking maybe it was frozen open. No luck. Still does it. I will re-charge the batts,try again. Its like whatever is supposed to tell the thing to stop trying to start, isnt telling it.

Somebody help me!! i am going crazy