Posting for a friend.

He has an '86 F250, and claims his starter keeps turning the engine with the key off, only way to stop it is by disconnecting the battery!

Electrical problem for sure, but from where? Gotta be in the ignition switch?

 

My first guess is a bad fender mounted solenoid/relay. I had a lot of problems with that on my 84 f150 until I broke down and bought a Motorcraft brand. I went through 3 off brand versions within 2 years. If you will do a search for "fender mounted solenoid" (with the quotes) I think you will find a test procedure for it.

 

Yep, 99% of the time, this issue is isolated to a faulty starter solenoid. The contacts inside can "weld" themselves together.
Every once in a while, there's another issue that causes it. Usually a short in the switch, or other switch fault.

 

Pull wire #5 off in the diagram above. If it still keeps cranking with this wire off, it's not the keyswitch.

 

If it is the solenoid after pulling the wire off, check the battery, low cranking voltage is the usual cause for cooking the solenoid.

 

I just had this happen on my 86 and it was the solenoid on the fender, and it took out my starter, still fighting the parts supplier on this for a new starter.

 

Probably a bad solenoid, but Ford does have a history of weak return springs in the ignition switch.

 

Thanks everyone, bad starter solenoid.

All fixed and working great!

 

Ok, I have a 1997 f-150 xlt 5.4L triton v8, about 2 months ago I started it up and the starter would not disengage, so i would have to shut the truck off and try it again and it would stop, just about 2 weeks ago I decided to do something about it, so I changed out both starter solenoids and my ignintion switch. but i still get the same problem, but now it turns over everytime the battery is hooked up (even without the keys out of it). I ran some tests on the starter relay fuse and some other wires. The power to the starter relay fuse is correct, (only power when key is all the way on) but even when there is no power to the fuse there is continuous power to the main power cable on the starter mounted solenoid, and im about to go crazy, i've tried everything. Can somebody help me????

 

Did you read the above posts? Do you have a wire that looks like #5 in the above diagram?

 

yup i did what the diagram said i replaced my solenoid, the relay, the relay fuse, and the ignition and it still does it...

 

and yes it did turn over with the ignition wire pulled off

 

#5 in the diagram is NOT an ignition wire per se, it is the wire that, when power is applied to
it, tells the starter solenoid to provide current to the starter motor. Red/blue stripe (at least
on gas engines) and should have power ONLY when the key is in the START position. Pull
that wire off the solenoid and do some tests.... that wire should have power only in START,
if there is power at any other time then the column-mounted ignition switch is suspect
(assuming no wiring problems between those two devices).

It sounds like you've got that much figured out... if there is power to the starter motor
anyway, that relay is defective and is sticking.

 

Yep, another stuck relay. I remember long ago someone figured out they were ruining the new solenoids by over-tightening the large nuts on the relay. The whole stud was turning inside the unit when they tightened it, making it stick. Other than that, it's just lousy quality solenoids(relays).

 

well ive put on 3 different relays while not snugging up the nuts and the problem is still there and i also had my alternator tested at napa and they said it is perfectly fine.