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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.

This behavior is by design and it was the same on pretty much any Ford of that era (at least it was on the Mondeo, Fiesta, Fusion and Focus IME)

You can modify it to come on with the ignition but not without a little bit of re-wiring so it depends on how comfy you are with some basic electrical work.

Essentially you need to wire a relay into the the 12V wire for the cigarette lighter and use something that is only live with ignition on as the trigger wire for the relay (the "ACC" wire running to the radio is a good candidate).

While not particularly complicated electrics I'm not sure I'd recommend it as a DIY job to someone unfamiliar with electrical work in general - the upside is that any auto electrician should be able to do something like this for you in less than an hour.

I believe this would need custom wiring to be switched on and off with the ignition. Your factory lighter socket is not wired to do this.

I do not like making modifications that change the factory wiring or can not be easily reversed, so this is my suggestion. Get a fuse tap. This will allow you to create a new circuit off an existing fuse. Use a switched, non essential circuit, like switched power for the radio. Run the fuse tap to a new 12v lighter socket. The power wire runs to the center back or the lighter socket. You will need to run a ground to the case of the lighter socket.

Example of a fuse tap:
https://www.amazon.com/dp/B0146EB6OE/ref=psdc_15729671_t3_B0146EB8EM

New lighter socket:
https://www.amazon.com/Parts-Express-Cigarette-Lighter-Mounting/dp/B078SKG4L7/ref=sr_1_7?s=automotive&ie=UTF8&qid=1545327233&sr=1-7&keywords=lighter+socket+bracket

I'd look for a lighter socket like this with a bracket. You can use double sided tape (think command strips) to mount it so you are not making a permanent change.

Alternately, you could run power from the new circuit to the existing lighter outlet. This may be more difficult to run the power wire through the dash. If you do this, remove the fuse for the current lighter circuit, so you do not have a live wire hanging behind your dash.

EDIT: Based on Paulster2's suggestion. You could use a 12v to USB (socket, or mini) if your only intention is to use this with USB devices. My only concern with this is if it is designed to work with the fast charge feature on your phone. Some of these are available in a kit with the fuse tap.

Here is an example of one.
https://www.amazon.com/Spy-Tec-Hardwire-Fuse-Kit/dp/B01N686R48/ref=sr_1_10?ie=UTF8&qid=1545329628&sr=8-10&keywords=12v+hardwire+phone+charger