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Running 12G power wire through firewall for stereo 45W amp

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Running 12G power wire through firewall for stereo 45W amp

 
Old 02-28-2019, 02:34 AM
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colter
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Default Running 12G power wire through firewall for stereo 45W amp

I've already got an aftermarket head unit and speakers in my 89.

I had been thinking of installing one of those small 45W Class-D amps like from Alpine or Kenwood, etc. But since our cars run the stereo on a 10A fuse, you have to run new power/ground wires and put a 15A fuse on the power wire at the battery. I've read for a small 45W amp, you need 12G wire. Though I've read of some people instead tapping the cigarette lighter wire.

The nice thing on our cars is there is a 12V+ junction block behind the battery that you can connect the power wire to instead of bolting it directly to the battery. The question is where is everyone running their power wire through the firewall at with these small 12G wires? I've read of some who have cut a slit into the rubber sleeve of the grommet for the hood release cables (I'm guessing on the bottom so water won't get in). Then taping the end of the 12G wire to the end of a thin wire-hanger and then pushing the wire through the slit of the sleeve in the rubber boot of the hood release cables at the firewall, and then pushing the wire into the car.

Has anyone successfully done this? Is there even enough room inside that grommet with the hood release cables for a 12G wire to fit through?

I can't really find much info on this as I really don't want to bother drilling through the firewall or running wire around and through the door area.

The other thing, is the small amp plus wiring would be around $150+. Is there really a noticeable improvement in sound quality to justify the cost and time of running power/ground wire? I know these small amps aren't about increasing the volume, but making it sound better and letting you turn it up higher without distortion.

Those small amps generally get good reviews. But I've also read some say the improvement in sound quality wasn't really worth the price, i.e. the improvement wasn't really all that noticeable.

Here's a pic of the sleeve I'm talking about. The sleeve part sticks out into the engine bay:



A view from the other side. It looks like there might be enough room for a 12G wire to fit through the inside white grommet:

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Old 02-28-2019, 02:55 AM
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If I remember right there is a 12 V tap underneath the console where the seat switches are for accessories and such. I donít know what the fuse rating is on that circuit but it is worth checking out because it is a convenient point of connection for a small amp.
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Old 02-28-2019, 08:32 AM
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Connecting to the battery is INO easier, because you have a space that can be easily accessed for the fire.

I ran my power wire through the big wiring grommet on the drivers side. It was pretty easy.

I wouldnt waste my money on those tiny micro amps. Spend the same money on a little bit bigger amp, it will make more power and sound better. They're not significantly harder to hide than the little power pack style amps, as those are actually large enough to not fit most places in a c4.
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Old 02-28-2019, 02:11 PM
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Originally Posted by FAUEE View Post
Connecting to the battery is INO easier, because you have a space that can be easily accessed for the fire.

I ran my power wire through the big wiring grommet on the drivers side. It was pretty easy.

I wouldnt waste my money on those tiny micro amps. Spend the same money on a little bit bigger amp, it will make more power and sound better. They're not significantly harder to hide than the little power pack style amps, as those are actually large enough to not fit most places in a c4.
Actually, I only looked at adding the small 45W amp because I thought it was plug and play. Then later I learned I would have to run a power wire and really didn't feel like messing with it anymore. As I really had no plans for installing an amp. Also going bigger amp, I'd have to replace my speakers, which I have no plans on doing. So originally I thought this would be a 10 minute install.

Do those little amps make a $200 improvement in sound quality? If not, then I won't bother messing with an amp.
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Old 02-28-2019, 04:08 PM
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Originally Posted by colter View Post
Actually, I only looked at adding the small 45W amp because I thought it was plug and play. Then later I learned I would have to run a power wire and really didn't feel like messing with it anymore. As I really had no plans for installing an amp. Also going bigger amp, I'd have to replace my speakers, which I have no plans on doing. So originally I thought this would be a 10 minute install.

Do those little amps make a $200 improvement in sound quality? If not, then I won't bother messing with an amp.
Not at all. They make less improvement than spending $200 on speakers wisely.
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Old 02-28-2019, 04:55 PM
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Originally Posted by FAUEE View Post
Not at all. They make less improvement than spending $200 on speakers wisely.
What type of speakers are you referring to?

I've got Alpine 4" in the front and Alpine 6x9" in the rear.

I didn't go with super high wattage speakers as I've read it's not good to run high wattage speakers off of the power from a head unit.

I am putting in a new Kenwood head unit.
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Old 02-28-2019, 05:03 PM
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I’m not up on c4 vette’s but in c3 vette’s there is spare terminal positions in the fire wall bulkhead fitting .
4 or 5 56 series and two 59 series
its a look to see if there is a spare entry in the c4
Bfit
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Old 02-28-2019, 05:14 PM
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https://www.crutchfield.com/S-mNasm5...KAC-M1804.html
if this is the amp you are talking about, it is a very nice little amp. i have the same one in my silverado pick up, you should be fine tapping into the cig lighter wire for power with an inline fuse . pretty sure that's what i did with mine
45 watts rms for 4 channels, 100 watts peak power, most new stereo's come with 20 watts rms per channel but this little amp is double that and clean power, i plan on doing about the same thing with my 91 vette but i think i want polk db series speakers for it. should be plenty of really good clear music.

in response to --Do those little amps make a $200 improvement in sound quality? If not, then I won't bother messing with an amp.--- you might not really see much improvement from amp alone IF the speakers are old and tired or with speaker surrounds that are breaking apart, it will sound not so great and maybe even worse with more power, you ever hear a speaker blow? sorta sounds like tinfoil getting wadded up lol. i would suggest a new set of nice polk speakers with that amp. you might have 600 bucks into the whole thing and i can almost promise you, then... you will be smiling and think yeap was worth it

Last edited by bud40oz; 02-28-2019 at 05:24 PM.
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Old 02-28-2019, 05:23 PM
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Originally Posted by colter View Post
What type of speakers are you referring to?

I've got Alpine 4" in the front and Alpine 6x9" in the rear.

I didn't go with super high wattage speakers as I've read it's not good to run high wattage speakers off of the power from a head unit.

I am putting in a new Kenwood head unit.
Speakers that can take high wattage tend to have lower sensitivities, which is more like and efficiency rating. So they dont tend to be as loud off low power.

Decent low wattage alpine speakers can still benefit from a larger amplifier pushing them. You also have to decide what you want out of it. Among your speakers will give you a little more bass, but mainly volume as you have very small speakers in thebfront. If you want bass, adding a small powered subwoofer would be the best path forward.
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Old 02-28-2019, 05:35 PM
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yes like FAUEE said look for the sensitivity rating. you want something like these here https://www.crutchfield.com/p_107MM6...o-MM-6502.html 93 db rating compared to some other speakers with 87 db rating. for every 3 db it doubles the loudness i think so going from an 87 db speaker to a 93 db speaker. you are increasing the sound level twice and will be a whole lot louder with much better speaker response at low wattage
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Old 02-28-2019, 10:08 PM
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Getting 45W from a 12Vdc supply only requires a 4-5A pull, needing far less than 12ga wires.
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Old 02-28-2019, 10:19 PM
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Originally Posted by 65Z01 View Post
Getting 45W from a 12Vdc supply only requires a 4-5A pull, needing far less than 12ga wires.
All the makers of those small amps all say that the power supply has to be on a 15A fused wire. They say if your radio's power is on a 10A fuse, then they say you have to run a power wire with 15A fuse from the battery and run a separate ground wire.

The maker of the amp, and other places I've read said to use a 12G wire for the power and ground.

So I'm just going by what the amp makers say to do.
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Old 02-28-2019, 10:36 PM
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Originally Posted by 65Z01 View Post
Getting 45W from a 12Vdc supply only requires a 4-5A pull, needing far less than 12ga wires.
Sort of true...

Its very simple to calculate (we will ignore losses). 45Wx4 is 180W total. We will assume 12v, though really while the engine is running we should be closer to 14V. 180W/12v = 15A. This is of course, a perfect world with 100% efficiency in the amp.
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Old 02-28-2019, 10:53 PM
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Has anyone fit a 12G wire through the rubber sleeve, and through the grommet of the hood release cables at the firewall?

I may just get some 12G wire and cut a slit or use a drill to try and safely drill a small hole into the bottom of the rubber sleeve and see if I can push a 12G wire through into the car.
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Old 03-01-2019, 05:53 PM
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I ran 8 gauge through the wiring harness grommet. 12 gauge is tiny. I wouldnt tun anything smaller than 8, 8 is small enough to be easy to run and can power a decent amp.
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Old 03-01-2019, 07:13 PM
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Originally Posted by FAUEE View Post
I ran 8 gauge through the wiring harness grommet. 12 gauge is tiny. I wouldnt tun anything smaller than 8, 8 is small enough to be easy to run and can power a decent amp.
What year and what wiring harness grommet are you referring to? On my 89, I don't believe you can put a wire through the wiring harness plug that is behind the battery. As it's a plug.

Looks like I'm going to have to try and see if it'll go through the hood release sleeve/grommet. I don't want to go larger than I have to as I don't think there is a lot of room in that grommet. I was just looking at running one of those 45Wx4 small amps. I wasn't looking to run some big amp as I'm not going to be pulling carpet and all of that.

On those small amps, you just need a 12G wire, from what they say. If your stereo is on a 15 amp fuse, then you can use the stereo power wire to power the small amp.
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Old 03-01-2019, 08:08 PM
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just connect that amp without adding any wire to the factory positive lead that comes with the amp to the cig lighter wire and stuff it in the tightest spot it will fit behind the dash and call it good man, trust me if it fits in there you will be fine, like i already posted i use that same kenwood amp in a silverado truck, stuff directly behind the stereo. has worked flawlessly for 3 years now. the farther away from a power source you run it, the bigger gauge wire it needs, if its hooked right up close to the power source you don't need any larger wire than what it comes with, which it comes with tiny small like 14 or 16 gauge wire on the factory harness for the amp, out of the box. it's kind of rediculous to hook up a 14 gauge wire to 8 gauge way over kill imo. even on my 1200 watt sub amp for the truck i only ran 10 gauge and it works fine.

Last edited by bud40oz; 03-01-2019 at 08:13 PM.
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Old 03-01-2019, 08:13 PM
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My firewall looks like swiss cheese. Just drill a hole and use a grommet. An 8, 10 or 12 gauge wire is small. I even have a couple 1 gauge cables for my rear mounted battery.
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Old 03-01-2019, 08:17 PM
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Originally Posted by colter View Post
What year and what wiring harness grommet are you referring to? On my 89, I don't believe you can put a wire through the wiring harness plug that is behind the battery. As it's a plug.

Looks like I'm going to have to try and see if it'll go through the hood release sleeve/grommet. I don't want to go larger than I have to as I don't think there is a lot of room in that grommet. I was just looking at running one of those 45Wx4 small amps. I wasn't looking to run some big amp as I'm not going to be pulling carpet and all of that.

On those small amps, you just need a 12G wire, from what they say. If your stereo is on a 15 amp fuse, then you can use the stereo power wire to power the small amp.
i have worked in a fleet fab shop for 25 years and now am sort of the stupervisor.. trust me when i say, do not run wires through those factory rubber grommets, thats just sloppy shoddy workmanship and i would fire someone for doing that. if you absolutely have to have a wire hooked to that power stud by the battery, drill a damn hole through the firewall and install a small rubber grommet, use plastic split loom over the wire and make it look as professional as possible, but still... hook it up to the cig lighter, jam it in any spot it will fit behind the stero in the dash and forget its even there
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Old 03-08-2019, 12:36 AM
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I think I'll start off with getting an Exacto knife and cutting a small "+" plus sign in the bottom of the rubber sleeve for the hood release cables at the firewall. Then taping the end of the 12G power wire to a straightened out wire coat hanger and see if I can push the wire into the car.

The Crutchfield 12G power amp wire set is a little thick on the insulation. If that wire doesn't fit, then at the parts store, they have some red 12G wire that has a lot thinner insulation. Instead of getting a new fuse holder for it, etc. I could cut off most of the thick wire on the fuseholder on the Crutchfield power wire set. And then use a heatshrink butt connector to connect the thinner red 12G wire to the thicker wire on the fuseholder. That would then hopefully be small enough to run into the car. Then I'd put a black plastic wire protector sleeve around the power wire to cover it up and protect it. This is if the thick Crutchfield 12G power wire can't fit through the grommet of the hood release cables.
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