[stevenva]

If it's just a few wires or even thick cables it's not too difficult. I use an old antenna which has a sharpened tip to poke through grommets. A coat hanger will substitute. Care must be taken to avoid poking into looms or anything that can't get nicked. Tape the wires to your wire fish. Lubricate the fat part you taped up so the wires slide through the grommet.

 

[ursubpar]

I used a tire plug cutter/filer to make the hole in my firewall grommet and pulled a 0 gauge cable through it. The grommet is very tough and I poked a fairly small hole, required me and another person to push from one side and pull the cable from a coathanger wire through the other.

 

[Phillyjudge]

Thank you! Still nervous about nicking something through the firewall.… Still curious about the fender liner option.

 

[Overlandlouisiana]

Bite the bullet and go through the firewall. Your chances of getting water into the car from the firewall are much less and you can also access it easy enough to seal your work properly after the surgery. Proceed….just be cautious.