Where is hole in firewall?

Any holes made by the factory are going to be plugged, as they don't want fumes and mice and fire getting through the firewall. You can make your own hole all you need is a drill, just be sure to use a grommet to prevent frayed wiring and pack the hole to keep out those fumes, mice and fire.

PS if you run a power cable direct from the battery be sure to use an inline fuse. I buy at insurance/salvage auctions and have seen to many cars there because of fires caused by added electrical circuits not properly grounded or with fuses.

A note on installing an inline fuse. Always put the fuse as near to the battery or power source as practical. The fuse ONLY protects from the fuse to the device you are powering. It will not protect the power cable from fuse to the battery. I have seen a couple of dummies run a wire from the battery to the trunk and install the inline fuse there and that is a very poor way to do it.

Thanks for your great responses guys. I am using a fuse that came in installation kit. But I wanted to know if Anyone ever ran a power cable through an existing hole in firewall...being a lease and all id prefer not to drill additional holes.

Find a rubber grommet that factory wiring goes through and carefully poke a hole in it and run your wire, when lease ends just remove wire and put a dab of silicone on the hole to seal it up. They will never see it.

Bought an amp installation kit and saw it came with a grommet for the power cable, so convenient. I also bought a line output converter box. After seeing videos of corse. Any of you ever used one?

Another way to not go through the fire wall is to run wire along a protected part of the frame ( you may see other wires run this way). Just make sure you avoid moving parts, and hot zones like catalytic converters or other exhaust parts. This is sometimes easier than running a wire under all the carpet, etc. Sometimes you can even hide the wire in existing wire looms, or buy your own protector at auto parts stores. (Looks like mini black corrogated plastic tubing with a cut running lengthwise to place your wire in). Hope this helps.

I just ran wiring for a led light bar on front of my truck. If you take a flashlight and look 3 inches above power booster and 3 inches to the passenger side and you'll find a factory hole about 2 inches in diameter with a black grommet in it. You can't see it from inside of truck but it's there. 2004 Ford f150 xlt model.