You should readily be able find a relay in the autoparts store. Look for one that has at least 5 terminals. More is acceptable. The 5 terminals will be:
Most relays have a diagram on the top showing what terminal is what. A multimeter will assist you.
Wire the +12V on the relay to the switched ignition (fuse this). Ground the ground terminal. Run a (fused) wire directly from your battery to the common (not to be confused with ground!) Run a wire from the NC to whatever you want to power. Ground your device you are connecting.
Thanks for the help, but don't think this is what I am looking for. Probably my question is not clearly stated. Or I am completely misunderstanding the answer.
I have installed relays before and the wiring is not a problem. Example when power is detected on one leg of the relay it switchs power from the dedictated 12v supply to the device terminal. I installed a relay for my aux reverse lights that detects power to the normal reverse lights that then supplies power from a dedicated 12v line to the aux lights.
This instance is a reverse of a normal relay. I want power to be supplied to a device when I turn off the ignition and when I turn on the ignition power is switched OFF to the device.
What are the definition/functions of NO and NC terminals as you describe?
NC = normally closed contact when the coil is de-energized, such as when the relay is at "rest." Sitting on a shelf, switched +12V power to the coil removed, etc.
NO = normally open contact when the coil is de-energized, such as when the relay is at "rest." Sitting on a shelf, switched +12V power to the coil removed, etc.
With your device wired to the NC, it will only be powered when no voltage is applied to the coil. When you turn your ignition ON, the relay energizes, the NC contact opens, and your device is switched OFF.
Guys, thanks for the help and very understandable instructions. I never realized that a relay worked in "both directions". Perfect solution.
Mudchucker - this is for the power/battery charger for a clip on Bluetooth phone rearview mirror. Currently I pulled a line off the cigar lighter into the overhead console and connected to the short pigtail power connector for the mirror. The "problem" is that when it is in the charge mode (when the ignition is on) it has two alternating/flashing red and blue lights at the bottom of the mirror. I can live with it, but the wife about wet herself when she drove to the store sunday morning. Kept thinking she had a cop behind her. LOL. When the mirror is running on its internal battery, there is just a small single blue light indicating the Bluetooth is connected to the cell phone.
For those of you that haven't seen these mirrors, they are an economical alternative to the aftermarket UConnect system. Have found only one drawback/flaw. They are currently designed for the European/Australian market and the FM modulator for using the truck stereo speakers only tunes to even number frequencies (89.4) and US FM radios tune on odd number frequencies (89.3, 89.5). Here's a link about the product.