engine won't shut off with key out!!

After my girlfriend jump-started a friend with our 78' gt, the alternator died. I replaced the alternator, instead of the girlfriend, and now the car stays running after the key is removed. I have tried a third alternator, with reversed wires to the alt. plug, but the same result.
The charge light remains on when the car is running, but the guage needle stays in the middle at all times. The alternator is the two wire type, ( the green connector has a blue and a green wire in the harness, and the 12v wire to the 10mm stud is white.)
The good folks at westbay auto tell me that in 1978, toyota began offering both internally and externally regulated alternators, as well as changing the polarity of the wires leading to the green connector on the back. I have tried both types, with the same results.
If anyone has any ideas, I would really appreciate some feedback!!!
I am completely stumped!!
Thank you in advance.

its probably your ignition switch