VERY CAREFULLY, I located the electrical wire boot that went through the firewall, used a pick to penetrate the boot, then fished a wire through with cable attached to it, had to do it a couple of times as cable kept coming off until I greased the cable, very snug fit as rubber caused a lot of friction. Have to be careful to stay on the outside of boot and not penetrate any existing wire or could be in big trouble. Picture enclosed.