Very simple..... Going through firewall. On both sides of firewall from engine side there is a round rubber through which you can see some cables going through. There are nipples that are not used. Just cut the nipple and route the cable. I started with a skinny wire to which I have tapped bigger and pulled it through.
Regarding removing the door cover. Start from front side and remove the piece which turns upward. All you have to do is pull hard to make it pop.
I hope this help.....