running the power wire

You should have a huge grommit in the firewall where your electrical wiring goes from under the hood into the vehicle. Take a flashlight and look to see if you see any factory grommits. I personally dont like to drill into the firewall UNLESS I have to. If you can find a big grommit, either try poking the power wire in along side of the other wires OR if the hole wont stretch, you can cut another hole next to be being VERY cautious though. Then remember to run your power wire down the opposite side on the vehicle than your RCA cable. I always run my power wire down the driver side and the RCA's down the passenger side.

" I always run my power wire down the driver side and the RCA's down the passenger side".

Many vehicles the battery is on the passenger side. Why extend the power wire another 5 to 8 feet across the engine compartment? Sometimes you can't seperate power and signal. You can try to cross signal and power at 90deg. or keep them isolated but that's not the real world. Radiated noise can occur, not 100% of the time.

Pull back the carpet, remove the panels and see what makes sence. Evaluate the firewall and see what's what, look under the vehicle and get an idea of the layout. Check twice, drill once.

Most American cars I've seen have the battery on the passanger side of the engine bay, while imports tend to have it on the driver side - I'm not a professional installer or anything, but this tends to be the case on the cars I've worked on.

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"I'm finished!" - Daniel Plainview

then ... the Germans add the trunk battery, usually on the passenger side. It does make life easier!