not tap to brake lamp wire but dawn light/lampu ujan/lampu kecik (what so ever they call) wires. So the marker will light up together when u switch it on ..not when u brake.
rear fog lamp you say? Hmm, plug out the cable of the brake light. Should ve located in a boot, switch on the lights, then try to use multimeter and see, which one makes the needle jump to 12v or below, then that is the one.
Wires should be given right? Just switch off the lights.
Splice the wire, long long spliced will be better. until u can see the copper/iron wires in it.
Poke it in to the hole u tested out. Then tape it around so that u can still poke in to the socket. And rmbr to tape the expose metal wires. To prevent electric shocks or blowing fuses.
Then carefully plug it in. The above post should be better. More advanced sifu.
I don't suggest u splicing the ori brake wires because i think thats harder to determine and abit messy, and also if new car, MIGHT void warranty.
Hope u understand
cheers.