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The vehicle in question is a 1997 F150 with a broken ignition switch. Inserting the key and turning it just spins. "Fortunately", the switch was left in the "on" position; the steering wheel is not locked and when the battery is connected, all the instrument panel lights come on just like they would when turning the key to the "on" position.

What I'd like to do is get the engine to turn over and hopefully start so the owner can take it to a professional to have the switch replaced without having to get it towed. I shorted across the starter solenoid and got the starter motor to run, but it's just spinning itself and not engaging the engine. Is there some sort of electronically-actuated clutch between the starter and engine that I also need to power? I could not find any other electrical connectors to the starter motor assembly.

The vehicle is not new enough to need a key fob to start, bit in any case, the original (mechanical) key is present and in the key slot.

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Not sure that I understand your issue. Did the ignition switch stop working? Are you just trying to bypass the ignition? –  Seminecis Sep 2 '13 at 23:20
    
See the first two sentences. The ignition switch does not work. It's mechanically broken and stuck in the "on" (not "start", so no cranking) position. My aim is to start the vehicle to get it to someone who can repair it without the need for towing. –  R.. Sep 3 '13 at 1:17
    
Sorry... read it wrong the first time. –  Seminecis Sep 3 '13 at 4:44
    
If it's a manual transmission, do you have the clutch in while shorting the starter? If that's not it, do you think the ignition is stuck all the way on for sure or might it be turned only to acc.? –  Seminecis Sep 3 '13 at 4:57
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It's an automatic. The instrument panel lights for alternator charging level (batt), oil pressure, etc. come on which I'm 99% sure do not come on when the switch is just in the "acc" position, so I'm fairly confident it's "on". –  R.. Sep 3 '13 at 5:35
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up vote 4 down vote accepted

I tried again, this time connecting the positive battery lead to the low-amp solenoid input terminal (which was harder to reach -- that's why I didn't try it before) instead of directly to the starter motor, and it started just fine. So presumably the solenoid must be actuating some kind of mechanical linkage between the starter motor and engine rather than just acting as a relay for the motor.

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