Can I shut off the entire electrical with the key?

[SteveM]

I have an electrical drain I need to track down (it might be the aftermarket turn signal I installed last year), so I have to remember to pull the fuse when I park.

Also, I keep leaving the turn signals on, and I worry that I might leave the dome or dash light on and kill the battery. Too many times of doing that, and it's off to the store for a new battery.

Is there any way to actually have the key turn the car off?

I have a repro key switch that looks like a popout, but isn't.

Would I just hook up a relay to the switch and run all the non-ignition connections to the battery thru the relay contacts? I can hide the relay in the kick panel (or even just have it under the hood).

Has anyone done something like this?

Car is not a show car, just a fun driver, so points are not important.

Steve