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Factory Amp Bypass (How-To)

28850 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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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?
My rear door speakers are doing the same thing. They sound like really quiet sub-woofers.
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...
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'm sorry if i misunderstood.
You have provided some very useful and, in my case, timely information.

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 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.
This gets my vote. As soon as I have time I plan on looking into it. I need to take a closer look at the wiring diagram you provided early in this thread. If it identifies a power switch of the amp, I may just see if any wires the Metra harness (or whatever I find in my dash) isn't using have continuity with that wire.

Edit: I took a closer look and it seems to just have a one positive power wire. There must be a relay somewhere. I'll at least check to see if it has voltage. If it doesn't I'll run some to it temporarily just to see what happens.
I went out to my van today and pulled the side panel off. After removing two screws in the door jamb, it came off just as easily as described in the first post.

I tried a couple of things:

First listening to rear door speakers before and after unplugging the amp. There was a definite loss of bass sound when the amp was unplugged. The amp may not be doing all that could be hoped, but it is doing enough to be noticed.

Next I took a multi-meter to the plug and discovered that both the positive and ground are always on. It doesn't make any difference where the key is or is not located. This caught me by surprise. It was not what I was expecting.

I now have two new guesses:

First, the amp must turn it's self on when it detects voltage on the rear speaker wires coming from the head unit. Those are the only other wires going into it and if it didn't turn it's self off somehow, it would drain the battery.

Second, I'm starting to wonder if maybe after market head units might have some soft of low filter. That would filter out most of what the factory amp is trying to amplify.

I think that a better description of what the amp is supposed to do is needed.

BTW, does anyone know what the impedance of the factory speakers is? Are they 4 ohms, like almost all car speakers, or something wacky like sometimes get used by manufacturers?
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OK, 3 ohms is [Edit]isn't[/Edit] that wacky.
Did you use an amp with a speaker lever input?

Where did you find that?
A complete wiring diagram it may be useful for who knows what else.
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