Hey guys I have a question. I am putting an engine in a friends 73 351c mustang. It went in great and starts great but when I turn the key off it keeps running. what did I do wrong. I reconnected the harness that was already there and did not modify anything. any suggestions??

 

Welcome to the forums! It sounds like the starter relay is not grounding to the body. Make sure it is snugged up to the inner fender. Good luck!

 

My friend had this problem with his 68. His ignition switch was messed up. How old is the ignition switch?

 

not sure how old the ignition switch is but the starter relay was put on when I put the engine in. Does the starter cable mount to one side (large terminal) and the battery posative to the other large terminal? I have never done a ford swap in one of these cars before.

 

You are correct on that. One item to check, there are two small terminals on the starter relay, s and i, if the car starts normally, that is doesn't try to crank as soon as the key is turned on, they are wired correctly. Try disconnecting the i terminal after turning the key off, it is the ballast resistor bypass, if the engine stops, replace the relay. It was not an uncommon failure of these.

 

I had this problem on my F100. If I pulled the "I" wire from the solenoid it quit. I replaced the solenoid with no effect. Found out there was a bad diode in the Alternator back feeding the ignition circuit.

 

Sort of a stupid question, but I started the car without throwing the alternator belt on...(did not get one yet), just to see if it starts. Could this be the problem? I will try to get a belt today and will then try putting the old starter relay back on. Talk to you guys soon.

 

you were right guys, when I put the old starter relay back on the car shut off fine. Must be a faulty relay. Thanks for the help! Adding a belt did not hurt either!

 

Glad you found it, welcome to the forum. FYI the belt doesn't matter- it just spins the alernator so it charges the battery.