HELP--Motor won't shut off!!!

[northern buick]

1957 Buick Roadmaster, 364 Nailhead, carter 4 barrel, car runs great, but, when hot (not excessively) after a long drive, I turn the ignition off, my gauges shut down, but the engine continues to run, smooth as silk. To shut it down I have been disconnecting the negative battery cable. Once you reconnect it the car starts as it should and runs beautifully!! I thought I had it fixed after I took the ignition switch apart and cleaned it but I think it only seemed fixed because the car was cold.
Anyone have any ideas about what I should be looking at? (Not another car):

[rogbo1]

Ever see the movie "Christine".?
Does the radio turn on by itself too?
If it has power seats, be afraid!:laugh:
Talk nice to it.:TU:

[Truzi]

Odd that it runs smooth when you turn it off. If it is dieseling, you can leave it in gear when you shut it off - that should be enough of a load to kill it.

If this is the case you need to get things fixed soon - fuel and cooling system.

If it is not dieseling, well, I'll second Roger's comment.
Then you'll have to look into the electrical system.

[sailbrd]

Have you upgraded to an alternator?

[buickgs464]

i'll go one better,hav'nt worked on that old stuff in a long time.i would look at why the coil is staying powered up.possible r-terminal on starter shorted to power,ignition switch? try using a test lite,hold it on the positive side of the coil,shut key off,see if coil is powered up still.good luck,dan