Adding a device in "Ready State" only

I bought a power inverter that I'm going to mount to the black tray, and run outlets to a more usuable location.

The problem is, if I forget to shut it down, I will kill my 12V, and I don't like that idea at all.

I'm going to install it wired directly to the 12V battery, but I want it interruped whenever the car is NOT in Ready state using a relay.

Where is a good SAFE wire to tap in to for this? I know some wires would be better to tap than others, and I am hoping somebody has done this homework already and would be willing to share the info.

 

Thank you for showing me how vague my origional posting was. I have since edited it and made it clear as to my exact needs.

 

Two questions:

#1) Which one is easier? The armrest or the dashboard, I'm guessing the dash.

#2) Occasionally, I put my phone in the car to charge, since it only takes about a 1/2 hour. Is there another line that is "Ready State" only, but easy to find?

 

Hmmm...

I'd hate to say this, but if I have to, I will tap into one of the power outlets.

You did get me thinking...Are there 12V lines in the car that are seperated from the battery that come out of the inverter?

My friend that is going to help me do this install cannot help until our kid's school year starts up on the 4th day of the new year...I have until then to find the exact wire I want.

The other thing is output, and I'd appreciate input. I'm thinking about mounting one of those 3 foot long power strips to the bottom of the bracket that the cover over the cargo area rolls into.

 

The headlights turn off after the car is powered down. Its on a delay, but they turn off...

Would that help point me in the right direction?

 

I know and understand that but, after my wife has had the car I hit the power button twice, turn off the heat/AC, turn the temp to low, and adjust my mirrors. She just drives the car, sometimes killing 10MPG off my average. I also leave the car with the 12V outlet on for a half our at a time for an emissions free charge of a cellphone. Also, when weather is bad, I go out to a car while on the phone and someone in the house should not hear me. (UPS left my son's laptop by my back door in the pouring rain [for 3 hours] and didn't even ring the bell. [Found it by taking out the trash] Its his Christmas presant. He was home when I found it.) I will turn the radio on for background noise for me.

I do this stuff out of habbit. Relying on an instant change will not end up well for me. Becides, I know it can be done. It seems I am the first wanting something like this. I doubt I will be the last.

The delays are probably in the device. The dome will come on at any time a door is open, but will only stay on so long. This method will be used if I can't find a way to do it with the results I want.

My friend that is helping me is doing the holiday thing until the kids go back to school on the 4th of Jan., so right now I'm doing research. I have until then to make our labor shorter.