Car won’t turn off

[Dcreech0]

I appreciate any helpful input I may get from you all. I finally have my new to me 1971 240z running and idling on its own.
I decided to try and tackle figuring out why my gauges were not getting power. I went to the fuse box and found a fuse missing that I think supply’s power to the dash. I placed a fuse in this empty slot and, behold the three dash gauges are all functioning as they should. Happy and relieved I went to turn off the by turning the key in the ignition. Key all the way out of the steering column and in hand, car still is running…… puzzlers I go to the engine bay and remove BOTH battery cables from the battery and the car continues to run. Baffles and confused I pulled the ignition lead to kill the motor. 
what could be the cause of this? Only thing I did is install a missing fuse. With the fuse out of the box, the car will shut down when I pull the key. 

[SteveJ]

Has the alternator ever been changed out for an internally regulated alternator? The lamp (switched) wire can backfeed into the ignition. The solution is to use a diode in the alternator circuit on the appropriate wire to prevent the backfeeding from the alternator to the ignition circuit. http://www.zhome.com/ZCMnL/tech/280Alt.html

[Dcreech0]

I did install an internally regulated alternator from a 280zx. When I did this though I installed the plug that msa sells for this upgrade. I thought this was to make it a ply and play affair and had the diode inside….

[SteveJ]

12 minutes ago, Dcreech0 said:

I did install an internally regulated alternator from a 280zx. When I did this though I installed the plug that msa sells for this upgrade. I thought this was to make it a ply and play affair and had the diode inside….

It should have, but diodes can fail, or someone could have installed the diode backwards.  If you have an ohmmeter, I can tell you how to test the plug later. Right now it's time to work on my car.

[Zed Head]

Don't take it apart if you find out it's bad and don't want to fix it yourself.  I wonder if  @Zs-ondabrain is still out there somewhere.