I ran all new wires in my car...

The doors were tricky, I couldn't just pull them through by taping it/coathanger easy enough. I just popped the rubber boot on the door off, then popped the other side connected to the chassis. Then I threaded the wire through the door, through the boot and then through the chassis, it gave me a lot more room to work at getting it through the chassis and catching it on the other side. The rubber boot then just pops back on.