No, the lead carries 5V - USB voltage, not 12V car voltage.
(I guess you knew that but thought I had better make it clear to all as a mistake is costly.)
I took the silver ring off the end of the lighter socket adaptor, prised it open, soldered a black wire to the earth spring and a red wire to the base of the coil spring, chopped the rest of the coil spring off and then wired the black and red wires to 0 and 12V on the car. It's actually quite a decent converter inside so no point buying another one with wires if you can solder a couple of wires on that.
If its going on your MG then I recommend using a "fuse tap" and taking power from the ECU fuse in the main under bonnet fusebox - that doesn't turn off when you start the engine and in fact stays on for 4 minutes after you park so covers petrol station stops etc.
