The other day my brother was driving my 76 F-100 and the brake pedal/brake lights switch started hanging and ran the battery down. he tried to jumpstart the truck and all of the sudden the thing just kept on cranking on its own.

now im pretty sure its not a faulty starter solenoid because i replaced it recently, but whenever you turn the key to ON position it just starts cranking on its own and it nearly welded the jumper cables to the bracket we used for ground on the motor.

ive never had to replace one but im guessing that its probably the ignition switch? all the other wiring was working fine before he jumpstarted it. i dont think they cost too much but i would like to ask what to expect when paying for one and will my local zone or O carry one?

if anyones ever had this problem let me know, thanks for replies.

 

It worked fine since you changed the solenoid? Sounds like the wires on the solenoid may be switched on the start and ignition posts.

 

Gunsmoke460,
Interesting problem, but one easy to diagnose. Before removing the ignition switch, try this: Remove the control wire, red with blue strip, from the starter relay switch. This wire typically has a press on type connector. Turn the ignition switch to the on position. Place the lead of a multimeter, voltmeter, or 12 volt tester light in the connector that you removed, and ground the other end. If there is voltage on this line when the ignition is in the on position, the ignition switch is defective.

If there is no voltage on the line, or the starter still tries to crank, the relay is defective. You can try tapping on the relay with the handle of a screwdriver to see if it will release.

Please write back and let me know what you find.
Thanks,
John24255

 

i still need to charge the battery up but that sounds like a great idea. once i get it charged ill let you know what happens. Thanks

 

well took me long enough but i got my brother work on it, i never could get a battery charger but i found that for 6 dollars i could just go ahead and try the new ignition switch, so i let my brother replace it and then he tried to jumpstart it. he said that he had the same problem as before so i went out later and gave it a try and it didnt start cranking again. i found an old starter solenoid that still worked and put it on there, and no problems, it charged up and started.

im guessing it was just a crappy solenoid getting stuck, ive never had anything but bad luck with those and i carry a spare in my other truck because of it.

the funny thing was i replaced the solenoid about a month and a half ago so i didnt think that was it at first..... very crappy part in my opinion.

 

Gunsmoke460,
Glade to hear you're back on the road. I suspected that it was your started relay and not the ignition switch. However, since you said it was new, I thought it best to give you a tip to check it.

The starter relay has a copper disk in them. When you activate the relay, a magnetic field pulls the copper disk into contact with the two copper lugs on the sides of the relay. When you release the key, the magnetic field releases the disk, and it starts to pull away. When it does, an electrical arc is formed which sometimes burns the disk. At times,this arc can fuse the disk to the lugs, as it was in your case.

Typically, these things are fairly reliable. I have only experienced two or three go bad in my lifetime. However, if the started is drawing too much current, this can cause them to go out prematurely. Starters can draw too much current if the engine is not properly timed, binding, or the starter defective, or loose and binding.

You may be correct and you could have purchased a defective on. However, if you continue to have problems, place a clip-on amp meter on the line going to the starter and check the current draw while cranking. You can purchase one of these from Autozone for about $6-$7.

Best of Luck,
John24255

 

i didnt know exactly what was inside those things, thanks alot ill keep that one in mind if i have any more trouble