How to: Run a 4ga power wire through firewall for amps

[Bugsi]

(Applies to 1992-1999 models. If you have a 2000+, your battery is under the back seat, so there is no point in running a power wire through the firewall.)

Originally posted July 2007. There had been previous posts with photo of where to drill, but the links had gone stale. Judging from the number of hits my post got, it's valuable information.

(1) Remove the Maxifuse panel cover.
(2) Drill HERE:


The first layer is plastic, and it sits maybe .25" away from the steel firewall. I drilled a 1" hole in the plastic, then went smaller in the steel with a cobalt drill bit, large enough for my 4ga power cable plus a grommet. You HAVE to use a grommet!!

Questions I had, and their answers:

My question: What happens on the other side of that hole?
Its a big open area.
I understand I may need to remove the glove box, the airbag may or may not be in the way.
You do not need to remove the glove box because between the glove box and the firewall is the air bag. -And you don't need to remove the air bag.
But WHERE does it come in on the interior side of the car?
on the firewall side of the air bag, if you take off the footwell panel and look up (or drill the hole and just push the wire down, you will see it comes out right in the footwell.
Is it easier to route it down the driver's side channel?
No. [Route it down the passenger side channel.]
How do I locate the end of the wire after I push it through the firewall hole?
Take the multi connector off and the footwell thing off and put a flashlight on one end and look from the other, you will see the light. Haha.

After that, installation was simple. I routed the 4 gauge wire to the battery, with a fuse about 6" from the battery connection. I ran the power wire down the passenger side channel into the trunk to the amplifier. Mission accomplished.

[rockit-man]

Wish I would have seen this before I crawled under, over and through every inch of my fire wall looking for a suitable spot. I ended up fishing mine through the fender to the inside of the door, where I snuck it inside the flex boot. Sorry the pics are so blurry, a photographer, I'm not.

[surfnben]

Dude, you don't know how much this helped me! My son just upgraded his rice burning big muffler honda with a set of double 10" subs and an 800 watt amp, and I got his sloppy seconds, 12" MTX with a 400 W. The weekend will go much faster, now.

[Bugsi]

That's why I posted it! There was a whole other thread about the bolt at the battery terminal. You might run into issues there too. I used I think a 1.5" long bolt, with some oversized nuts and star lockwashers to connect everything. I'll link you to that thread if I can locate it.

Inside the car, I remove the plastic trim along the door edges along the floor. Remove the piece over the B pillar first to make life easier on you. It helps if you have a door trim removal tool in there. I always wind up busting some plastic, so I keep a generous supply of 2-part epoxy putty around for repairing it afterwards. It helps if you go slowly, carefully, and use a door trim removal tool. I run the wires in plastic wire loom tubing and route it along the channels where the other wiring harness loom runs along the base of the doors on the floor.

Good luck!

[radomirthegreat]

Bugsi, I had no idea it was you who wrote that. 1337ssei just told me about this, so we both have our firewalls drilled there. Thanks for this awesome writeup!

[calaeb0896]

is there anyway that you could get a pic of where to drill from the inside of the car? if not not a big deal but i was looking and i wasnt sure where to drill. About how long was the drill bit? and where do you get the groumets spelling?

[Bugsi]

is there anyway that you could get a pic of where to drill from the inside of the car? if not not a big deal but i was looking and i wasnt sure where to drill. About how long was the drill bit? and where do you get the groumets spelling?

I believe it is impossible to drill the hole from inside the car, and likewise it is not even possible to get a photo from inside the car, this is only accessible with a drill from the engine bay.

I drilled a one-inch hole in the plastic where the arrow is pointing, using a one inch hole saw bit. This can be a cheap, inexpensive wood-cutting hole saw, you'll only be going through the plastic with it. You might need to first drill a starter hole for the mandrel bit in the hole saw, and definitely do that first using a steel-cutting twist drill bit of perhaps 3/16" diameter, right in the center of where your hole will be. There is a gap of about a quarter inch between the plastic where the arrow is pointing, and the firewall steel behind it. The final hole through the steel firewall should be drilled with a suitable diameter steel-cutting twist drill bit, of diameter large enough to pass through your power wire with its insulation and a grommet. I might have even drilled a hole that was a little small, and then opened it up using a steel cutting bit on a Dremel tool. One of those stepped bits would be even better, but they're kind of pricey. You can buy wire grommets at Radio Shack in a 31-pack for $1.99, part number 64-3025:
http://www.radioshack.com/product/index ... Id=2103392

For steel-cutting drill bits, I use Sears Craftsman Cobalt bits.

You have to poke the wire through the hole from the engine side of the firewall, and it will snake down into the passenger footwell if you have the trim plastic removed.

[calaeb0896]

ok thanks!

[KERNSX117]

How far in do you think you have to drill? I have a decent size hole already drilled and is big enough to put the wire through and when I would push it through I could not find it on the other side. Any suggestions?

[Bugsi]

Only drill enough to cut the hole through the steel, that's all. Don't go shoving a drill bit around inside the hole and rooting around. When you shove the wire through the hole, aim it DOWN and shove it in there. If you can get a foot or so through, just climb in the car upside down and shine a flashlight up there from the footwell and your cable should be RIGHT THERE.

You did go through the steel, right? There's the plastic piece in front of the steel (from the engine bay side), and you have to go through both the plastic and then the steel. You did that, right?

[97SEBonnevilleMan]

Aloha
Thanks for the info about mounting the power wire through the upper part of the firewall.The lower area is to filled with heater hoses etc.There really is nowhere to mount your fuse holder near the battery in my 1997 SE Bon.
I tried the second idea of mounting the 0 gauge "Streetwire is what I am using" through the fender hole,then through the grommet on the front passenger door then down to the floor to the trunk.I do not know if this will create any noise with the wire from the door location in the same area.I ran my RCA's "Streetwires Zero Noise "through under the center console/carpet and speaker wires to the the trunk. Now to figure where to mount my amp.....and capacitor.Let the Dynamatting begin......to Peace Matt

[Bugsi]

There really is nowhere to mount your fuse holder near the battery in my 1997 SE Bon.

Clearly it can be done, since I have mine mounted near the battery in my 1997 SE Bon.
[Edit]: Right here:

[97SEBonnevilleMan]

Thanks for all the pictures of everyones ideas
But ......to mount a 0 Gauge fuse holder where you show is a not going to work,I know I probally could have used 4 gauge power wire,but i'll figure something out .....

[TheNiceLips]

I know this is titled "through firewall"...but to complete the task at hand, how do you run the wires into the trunk?

I can't seem to pull the trim panel/scuff plates all the way off to run the power/RCA cables. I can get the power cable through the firewall, but get stuck at this point, because I don't know what the best method for running the cables into the trunk is...

Thanks in advance

[Bugsi]

The plastic door sill plates come off. They have plastic barbed "fins" that stick out of the back of them that fit into little metal clip slots. It's a real pain to pry the plastic sill plates out of the gripping metal clips, but that's what you do, and once you get them out, there are wire looms under there that run down a channel along the side of the car.

It is useful to pre-plan what wires you want to run where. I run my line-level audio outputs from my head unit down the driver's side, as well as the speaker wires coming from my trunk-mounted amp that drive the door speakers. I run the power wire and the amp turn-on wires down the passenger's side. OCD people like myself loom all of the wires in split-loom tubing, but you could just run the insulated cables without a loom if you insisted.

Once you get them to the back seat, take out your back seat cushions and run the wires into the trunk underneath the plastic flap of the rear seat support frame.

[BonneMe]

I mounted my fuse holder to the front of the washer bottle right next to the battery. Zip tied IIRC... lol.

If you can't (or won't) run a fuse on your mains, then carry a fire extinguisher, and pray you never have a problem.

Great spot/write up.

[Bugsi]

If you can't (or won't) run a fuse on your mains, then carry a fire extinguisher, and pray you never have a problem.

This is more true that I can even stress. For anyone who isn't clear on this: You should have a fuse on your main as close as possible to where the main connects to the battery. You'll be pushing some serious current through that cable, and a short circuit on the main will attempt to push the entire energy reserve of the battery through it all in one instant. The result can literally burst the cable into flames and explode the battery, and that's if you're lucky.

[DaMaroon]

Never new batteries gassed when shorted until I walked into a friends garage and he had pulled the battery out of his MC by putting a wire on both terminals. Unhooked the wire and got it outside. Boy was it hot and fuming. Could've been the Hindenburg inside his garage. Then theirs the battery acid blowing everywhere.

A fuse really isn't optional!