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Factory Amp Bypass (How-To)

28831 Views 48 Replies 18 Participants Last post by  dethrok
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After scouring the web, I couldn't find a great How-To on bypassing the factory amp :banghead: . There are about 6 threads that cover all of it in sections, but it was a little annoying hopping back and forth trying to figure out everything. SO I'm gonna throw all of this stuff into one thread. (I'm sure as soon as I post this, someone is going to post a link to some great instructions, but whatever)

This instruction is to replace factory Delco stereo that you don't want anymore considering you haven't owned a CD since Brittany Spear's was #1 on TRL.

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I've wired in a Kenwood BT958HD. Bluetooth, AUX, 2x USB. I'm not going tell you anything about installing the Head Unit, considering there are a billion how-to's online, this write-up is going to focus on our special amp.

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Why bypass the amp? Well, everyone that's installed an aftermarket Head unit, has found that the rear door speakers stop working. The factory amp ONLY powers the two rears, so you should already have the two 6x4" tweeters on each tower working before this process. And pretty much every In-Dash stereo sold nowadays has a built in amp that should have no problem powering all of your speakers.

First off: Locating the amp:

The amp is sitting behind the kick panel just behind the driver' seat. It's easiest if you remove the first row seat so that you have room to work. It should pop right off without any tools, besides one small phillips just inside the drivers door panel. You'll have to unplug the little running light for the drivers door jam. You'll find the Amp in between the Gas Fill, and the rear wheel well.

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You can unplug the wiring harness and toss the amp out, You won't be needing it anymore.

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Step Two: Splicing the wires

This is the scary part. Use your wire cutter, and snip off every wire but the Orange and Black. These are what you'll be splicing together. You're essentially powering your rear doors and tower with the same channel from your head unit.

You'll be splicing these wires together:

Left Speaker:
+ Brown --- Dark Blue w/ White
- Yellow --- Light Green w/ Black

Right Speaker
+ Dark Blue --- Dark Green
- Light Blue --- Light Blue w/ Black

This Diagram will help you if you don't trust me:
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After splicing, snip off the orange (Amp Turn-on) and Black (Ground) and close them off. You No longer need these (Unless you want an aftermarket amp, these could be used for that (I think).

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Step three: Put everything back together.

It's as simple as that, I'm sure someone here that knows more than my *Extremely Limited* knowledge of electrical, has a better solution, but this seems to work. SO have at it!

P.S. I'm not responsible for someone blowing up their van while following my instructions. :banana:
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No Pics? Hmm... Showing up on my side. I'll try a new image host.
On it!
esc said:
That is good info. I have an aftermarket head unit, I'll have to go see if my rear speakers work.

Instead of cutting up the factory plug, I may just use a crimp in wire splicer to make the connections.
For that matter...I wonder what would be needed to get the factory amp to work?
You could try to make it happen, but it would be overkill. Your aftermarket H.U. should already have an Amp in it to power the rears. What really needs to happen, is Metra needs to make an actual clip that you plug right into the wiring harness off the amp, but we can't be that lucky.

Truthfully, I'm not sure why the factory amp stops working after installing a stereo.. but if it's as simple as connecting a turn-on somewhere, it may be worth looking into. Not sure if the speakers may be damaged though with Two amps trying to power them.
BuddyHuggs said:
There they are! Thanks for sharing this info with us. Is the project any different for those with the rear heat?
I can't imagine it is, you may have some stuff to work around to get to the amp though. I'm pretty sure the rear heat unit is posted up in front of the gas fill indent, so it shouldn't be in the way at all. You may have to move a heat duct to get to the amp, but I can't imagine that involves anything more than just lifting it out of the way.
esc said:
The speakers on the sides in back sound fine. Loud and full range.
The back door speakers are VERY quiet and don't produce anything over about 100 hertz.
I wonder if this is what leaks through the amp when it has a high level input?
I do have a box that modulated high level inputs to produce a low level output that can be fed into an amp.
I may play around with trying to get the factory amp to work...
You can give it a try, I guess if you already have the module it might work. But this is a free method, and after installing a new HU you don't need the amp anymore. :dance:
esc said:
I don't mean to detract from your walk though in any way. If it weren't for you bringing this up, I have no idea when or if I would have noticed my rear speakers were not working. In fact I may still do what you have done. But if there is a chance I can take two otherwise useless pieces of junk that i have laying around(factory amp and signal modulator) and turn it in to more power for the stereo I figure it's worth a try.
I wasn't being defensive, sorry if it came off that way. I've got an aftermarket amp powering my sub currently, but I'm actually pretty impressed with the sound of the stock speakers powered by my new HU. And of course, as I mentioned before, I'm not in any way an expert in electrical or car audio. But I sure have learned a lot with this Van and friends vehicles. (You think our amp is a pain, try working on a Tundra)
gavio said:
The rear door speakers are supposed to be subwoofers, they are referred to as such in the FSM.... WHen they are working the way the factory intended, they won't produce anything but low base.... I'm not saying it's the best way, but it's GM's way.... I never tried it, but I imagine if you ran a complete signal to them, they wouldn't sound very good in the upper ranges....
Not sure why they did it this way, or what their logic was, but after this by-pass I seem to have full range in the door speakers and it sounds just fine. I'm considering getting a new set of real speakers (not "subs") for the rears, but funds are going to the 100+ other projects I have going on. Not sure if there are any tech specs the recommend doing anything differently.
paulo57509 said:
Just a guess here, but in order to get the factory amp to work it probably needs to have a line level converter put in between the head unit speaker output and the amp input:

Or if the head unit already has low level outputs (RCA jacks), connect these to the amp.
This would work if you wanted to swap the Stock Amp with an Aftermarket one. - The Factory amp doesn't have RCA inputs.

EDIT: Nevermind, I see what you mean. This could very likely work. But only worth doing if you have one laying around. (Why spend money when there's a way to do it for free?)
esc said:
I'm a little confused.
If the amp is getting a signal that is split off of the center speakers, wouldn't that signal have already been amplified, not line level?
If it got a high level input in the first place why doesn't it just work?
I feel like there is some important piece of information missing in this puzzle.

Why does the factory amp stop working in the first place?
My only guess: And this could be way off.

The Stock Head unit doesn't have the power to supply the 4 Rear speakers in in the Back. So the head unit supplies what it has to the amp and the amp "boosts" the power to the rear (door) speakers.
- Interesting fact: IF you unplugged the amp, the back 4x6 tower speakers still work.

Which means, the main power is being run to the back Tower -at some point it Splits - Goes to the amp - then runs to the rear door.

My suspicion, is that since your Aftermarket HU is powered by an internal amp, there is TOO MUCH juice running into the amp and it just decides to stop working.


The Metra wiring harness (Which seems to be the only one available) Doesn't include the Amp (Turn-on) power. A solution could be as easy as hooking up a power supply to the factory amp. I considered this, but didn't want to run into an issue involving too much power from having two amps. This would be an easy test with a volt meter, but I had already started doing the wire-bypass and it wouldn't have changed my process.

If someone does this process, and wants to see if the Turn-On wire for the factory amp has power, I'd love to hear what the results are.
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biker80 said:
The rear speakers are spec'd at 3 ohms. Only bad thing with just bypassing the stock amp is the impedance doubles being drawn for the rear channel. That can cause a quick death of an aftermarket HU. The amp and rear speakers worked fine in mine after changing the HU, I changed to a aftermarket amp for the door speakers for tailgating and just had to run a remote trigger wire back to it. I also cut my doors out a bit and installed a set of 3 way 6x9's.
My HU specs are 4-8 ohms, So I did a bit if research to see how compatible that is for 3ohms. Biker80, let me know if you disagree, I'm just relying on what the internet tells me (So you know it's all correct) A few sites I've visited have pretty similar answers. But I'm still considering getting a set of 4-8ohm speakers to be safe.

Taken From Another Site: ... m-amp.html \/ \/ \/ \/ \/ \/

This may make you feel a bit better.

2 ohms, 4 ohms, 8 ohms is a nominal measurement. an 8 ohm speaker may dip as low as 4 ohms at certain frequencies and may go up to 15+ ohms at other frequencies.

That so called '8 ohm speaker' can look like anything from 4 to 15+ ohms to the amplifier especially if a passive crossover is used.

Point is, that 3 ohm speaker will almost never look like 3 ohms to the amplifier so its really no different then a 2 ohm or 4 ohm nominal speaker. Its just a general guide and as sonic007 said it will be fine. If the amplifier was running borderline hot to begin with it may cause a problem but that shouldn't be the case.

Overall a 2 ohm speaker looks like a lower impedance then a 4 ohm and that 3 ohm will appear slightly lower then a 4 ohm but nothing will care.

This may give you an idea of what I'm talking about.


Full disclosure: I have no idea what that graph says [\b]
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Sooo After a bit more research,

I found THIS!

It's hard to read, but it's the full wiring diagram for our van.

Good news! This means that our 4ohm rear Tower speakers and our rear 3ohm "subs" are wired in a series after doing the factory amp bypass. Meaning, we're creating a Total Impedance of 7 Ω per channel. (Thanks to this handy calculator: ... calculator)

So a common 4-8ohm aftermarket HU should have NO issues powering our rear speakers, and you shouldn't encounter impedance issues after this mod.

--- This is just my judgment after reading the diagram and drawing in the mod on my own. Please let me know if I've made any mistakes.
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Broseph said:
Thanks for the post. Having that wiring info made it sooo easy to bypass the factory amp! I removed all the stock stereo equipment and replaced. I put an amp under my new deck above the dog house. Instead of a plastic shelf replacement for the factory cd player I built a custom wooden shelf enclosure. While I was in there I also tackled an air hose problem, but that's for a different post!
Hell yeah! Nice work. Glad my instructions worked!
Broseph said:
I am actually going to put a rear speaker amp back in that spot, but it will have to wait....
I put my aftermarket Sub Amp in that spot, and wired in my 12" Sub. Sounds great!
Awesome Bobby! Glad it worked!
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