In my 2006 ford ka the cigarette lighter socket is always on, which means that when I turn off the engine I have to unplug the USB thingy I've got in there. It's a bit annoying and I'm constantly worried that I've forgotten to unplug it and I'll come back to a drained battery. I know that the battery probably won't drain completely overnight but it's still annoying. How would I go about making it so that this port only turns on when the car is on? I have things constantly wired into it so I need it every time I drive but only when I drive. Is it something to do with a fuse???

Thanks in advance.