note that if there is nothing plugged into the lighter, then it is not the source of the drain. The only way they can consume is if there is a dead short. They are directly to the switched hot 12V line (KL30) line. I do not have the exact fuse, but hopefully this reference can help you out. There are various diagrams. Just type in what you are looking for.
https://www.newtis.info/tisv2/a/en/f06-650i-cou/
Good luck