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1966 Ford Mustang Coupe
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Discussion Starter · #1 ·
So I have a 66 mustang and anytime i try and start it, it keeps cranking. I can turn it off by just turning the key to the off position. but if I leave it in the ON position the starter keeps cranking. Ive already taken the starter to auto zone to have it checked and it worked fine. My dad and i found that if we start it and while it keeps cranking we remove the "S" plug on the solenoid, it stops cranking and runs fine. is it my solenoid or something else? how can i find out?

all help is appreciated.
 

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1: does it have a vintage style starter? (as opposed to a newer style mini starter with it's own solenoid)
2: post a pic of your solenoid wiring. This may help figure out the issue.
 

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After market replacement solenoids are notoriously bad. They get stuck on.
 
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It sounds like your "S" wire is energized when you turn the key to the "On" position. You can verify this by connecting the "S" wire to a test light instead of to the solenoid. Then switch on the key to see if the test light switches on. The light should only be on when you turn the key to start and hold it. Anyway, assuming the "S" wire is hot when the key is "on", then you either have the switch wired wrong, or you have a short in the "S" wire, or your switch is bad internally.
 

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1966 Ford Mustang Coupe
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Discussion Starter · #6 ·
Kinda sounds like you've got the S and I wires reversed.
View attachment 762716
what do you mean? cause if i simply switch the wires, nothing happens. the car wont crank. weve tried that already. and its all original wiring although some if it seems to have been "repaired" here and there. Unfortunately, one of your intake valves was bent when we had it running so weve sent the engine blocks to go get done. the car had been sitting for about 15 years and we didnt take the proper precautions before trying to start it. there also seems to be something draining the battery. if i leave the battery plugged in, itll drain over night. im going to pull out the ignition switch out tomorrow and check the wiring.
 

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You could have an ignition switch going bad. I had this happen on a 68, and the entire wiring harness pretty much melted to the ground and went up in smoke (Underhood and dash). In my case the starter started to run on its own when I was driving the car. I had to quickly pull to the side of the road and pull the battery cable which actually pulled the wire out of the battery terminal as it was very hot). My advice, get this problem sorted out or deal with much bigger problems.
 

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Discussion Starter · #9 ·
ok, so i pulled out the ignition switch and replaced it. Havent had the opportunity to see if that fixed it because we are currently fixing up the engine. however, when i pulled out the ignition switch i noticed an extra set of wires attached to it where the ground normally goes. Its a yellow wire that leads to nothing, and another black wire thats taped to the yellow wire that leads to the engine bay but has been chopped off. does anobody have any idea what these wires are for? should i just remove them?

also, is that little bell shaped connection for a courtesy light?
763772
 

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Big yella is usually the main power supply for the whole electrical system. Seems someone has re-arranged things if the yellow one is disconnected.
 

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do you own a 12 volt test light?
 

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Discussion Starter · #14 ·
The Yellow and Black taped together are wires for an Air Conditioner. The Yellow provides power to the Fan switch and the Black runs from the Temp controller to the clutch on the compressor. Look at wires 358 and 359 in the lower left corner of the attached diagram. That center post in the back of the ignition switch is "hot" when the key is in the ON or ACC position.
Oh ok i see, well there isnt an A/C system currently installed in the car, will it be fine if i just leave it there? or should i remove it?

there are also other cables i noticed that are just unplugged and hanging around. idk if threyre supposed to be plugged in or if its fine that they arent.

763773
763774
 

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There are a lot of harnesses sold for these cars that work with other cars like Cougars, Fairlanes, etc. which had other options not available on Mustangs, so there might be some extra connectors that go nowhere on your car if it isn't equipped with options offered on the other cars. These aftermarket harnesses are easier to manufacture if they cover many cars rather than making individual harnesses for specific cars... one size fits all.
 

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Oh ok i see, well there isnt an A/C system currently installed in the car, will it be fine if i just leave it there? or should i remove it?

there are also other cables i noticed that are just unplugged and hanging around. idk if threyre supposed to be plugged in or if its fine that they arent.

View attachment 763773 View attachment 763774
As long as the wires are properly "terminated" then leave them be. By "properly terminated" the wire should have a insulated female bullet connector if it's "hot" or a insulated MALE if it comes from a particular accessory. If it's just a snipped off wire, I usually fold the end over and tape it up until I determine what it is and where it should go....just in case.
 
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