I have a 1968 f100 that is driving me crazy. Issue: Went to crank it and just got the old "slow speed turn from the motor", as if not enough juice to kick it over. Tried jumping it off but no luck, however, after I turn key off, starter kept stayed engaged and kept trying to start. How is this possible if key in off position? Solenoid? Switch? Wiring? I replaced solenoid, still no luck. Tried new switch, still no luck. traced wiring as much as I could but didn't see anything wrong. Would a starter cause this? If so, please explain. I do not understand how a starter gets power and stays engaged if key is off.
I have had this happen. First have the starter checked. Sounds like it is drawing to much current. Something is causing the solenoid to stick in the closed position. I know of only three things that will cause this.
1. The starter is drawing enough current to cause the contacts in the solenoid to get hot and stick.
2. 12 volts is staying applied to the start contact on the solenoid.
3. It is a crappy solenoid made in China or some such place.
Ford starters require a good 12volt supply to the starter. This means you should have a fully charged battery, a good solenoid and good leads between the battery and the solenoid and between the solenoid and the starter. The starter mounting bolts should be clean and tight as this is the ground. Also make sure the ground wire is good between the engine block and the battery neg terminal. Make sure all connections are clean and tight. Hope this gets you started in the right direction
I'd go with a faulty soleniod. If it was "bad" and the contacts weren't making good connection it would make the starter turn slow(like a dead battery). There again, if they did weld themselves together from being burnt too bad, it would allow the starter to continue cranking with the key "off".
Make sure you have good battery cables. I've seen ones that look okay, but the ends are almost broke inside the insulation. Only a few strands of copper holding them together.