trying to add some lighting in the foot wells and under the seats in my car so that when someone drops something down there in the dark, it's not something that (at least not every time) requires pulling over and grabbing a flashlight to see. LED strips are cheap as chips, so my thought is I would just tap a 12V power supply, but then thought about it more, and technically I would want these on in 2 cases:
1) If the headlights are on (would only have power while the car was running; essentially: if the dashboard is backlit, the foot wells should be lit as well)
2) If a the dome lighting that corresponds to whatever area is on (in my car, there's a light in front, and another in the back, so if you open the front door, I'd want the front foot wells lit; open a back door, light the under-seat lights)
I am able to put stuff together once provided with an example, and assume I need some type of switching device to make it so I'm not turning on dashboard lights when I open the door / blowing anything up, but, as of yet, haven't figured out what to do there. Any input would be helpful.
Best Answer
With limited information about the components you want to use, it seems like a "diode-OR" circuit (Wiki Link) could we a quick and dirty fix. If either the dashboard or the front dome lighting is on, the LED strip will be powered (minus the voltage drop across the diode). However, the dashboard will not power the front dome (or vice versa).
Basically, something like this, which you could obviously replicate for the back foot wells:
simulate this circuit – Schematic created using CircuitLab
Also, this assumes the LED strip is rated for 12 V and has internal current limiting features; or else we'd want to add a current limiting resistor in series.