I have a 70-M1 street driven all orignal car that ive owned for 25+ years. Has about 100,000 on it

every once in a while when i turn the key off the car still runs.

Im not talking about diesaling.  The beast idles like it was on and you can drive it way if the steering werent locked.

The only way I can shut is is going under the hood and rapping the starter solenoid

What could the prob be as the solonoid engages and dis engages fine when the key is turned.  
I replaced the sol and it didnt help any

its a very intermitant prob.

Cheers all  

Check out this post and link:
http://forums.vintage-mustang.com/showtopic.php?tid/1493125/fromsearch/1/tp/1/  

i had the same problem with my '67 mustang, change the solenoid.  

thanks Bill.  I'll give the switch a good cleaning over the w/e

I have some good eletrcial contact cleaner laying around the garage

Its funny though that rapping the sol. shut it down

Coincidence?????

who knows

ive been meaning to get under there anyways to bypass my resistor wire for the pertronix so i'll kill two birds with one stone  

Sounds exactly like the problem I had several years ago.  I could turn off the key and the car would continue to run normally.  I could remove the key, walk away, and the steering column would lock but the engine would continue to run normally.  The only way to shut it off was to let he clutch out in gear holding the brake firmly and it would kill it.  For a while I just installed a battery disconnect switch on the positive battery cable as I tracked down my problem mostly through new parts and pieces.  I replaced the ignition key switch, the solenoid, and installed new ground wires plus jiggling and wiggling any wires I could under the hood and instrument panel but my problem continued.

Finally I traced it down to the electric ignition switch under the plastic steering column cover on top of the steering wheel.  This is tied into the 1970 and newer steering column locking system.  I started looking for one but there was no repo part available for a 1970. You could buy 71 to 73's but no '70's. A NOS one (if you could find it) was going for $125 plus on e-Bay. I bought a used one at a Carlisle All-Ford show for $25. I took it home and cleaned it up as well as my old one with electronic cleaner and when I was through I couldn't tell which one was which. Anyway, the one I installed worked great and I haven't had any problems in three years.   The Ford part number is “DOAZ-11572-A”

Below is another link of a 1970 Mach 1 owner who was having a similar problem and the advice given to him:

http: //www.mach1registry.org/forums/showthread.php?t=82295


Good Luck  

I read Bill's comments and it reminded me to offer:
If you don't know, Ford had a recall for ign switches in the late 90's cause they used to short to ground and burn up the car.  May or may not be the case here, but its a real enough problem to have concern.  The switch replacement procedure is fairly straight forward once you gain access to it.