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Using factory sub amp harness on new amp with aftermarket HU

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March 22, 2015
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Year, Model & Trim Level
2000 Mountaineer 5.0L AWD
I have a 00 Mounty with the MACH system and I'm wanting to upgrade the factory sub, amp and HU. I've ordered an 8" sub, a small 200 watt amp and a new HU to replace the factory stuff.

My situation is that I want to do as little wiring as possible. Crutchfield recommends this harness (even gave it to me free with my HU)
http://www.crutchfield.com/p_120705517/Metra-70-5517-Receiver-Wiring-Harness.html

If I understand this harness correctly, it lets me connect Amp ground, amp turn-on, and one of the RCA outs of the new HU to the factory amp.

My first questions are:
1. Since it only lets me use one RCA, will my factory sub only play the left or right channel (whichever I plug that one RCA into)?

2. Is there a separate power wire going directly to the amp? If so, what gauge is it?
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Okay now to upgrade the stock amp and sub...

I have a mono amp, but, it still has 2xRCA inputs or 2xhigh-level inputs.

Since I'm only using one sub, I don't need it to be in stereo. Could I use something like this: http://www.crutchfield.com/p_979YRA105/Hosa-RCA-Y-Adapter.html to go from my HU to the previously mentioned harness with one RCA, and then split that back out into 2 RCA's on the other end by the amp? (I hope that makes sense) Or should I just run new RCAs from the HU?

The amp I'm installing requires a 12 gauge wire for the power, and the remote wire is already ran, if I can get by without having to run RCAs, it would be nice.
 



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Since the factory HU only has a mono output, and the factory amp only has a mono input, the adapter is probably just a mono plug because whoever designed the harness was assuming that a newer aftermarket head unit with a mono sub output would be used, even though most aftermarket head units still have stereo sub outputs.

You can use a Y-adapter to input the left and right sub outputs from the aftermarket HU into the single sub input of the adapter if you must use the factory amp.

There better be a seperate power wire going to the amp, probably something pretty small like 12-14 gauge.


Even when using a mono amp for a sub, it's not about anything being "in stereo" (which you would need two subs, one on each channel of a two-channel amp for), but it's about the sub getting the sub signals from the left and the right channel. If you just hook up the sub to one channel, just the left or the right, then you only get the bass signals from that channel. If there are bass signals in the other channel, the amp and sub won't receive them or produce them, and it can make the music sound weird.

If you have an aftermarket head unit with a left and right sub/rear output, and a mono amp with a left and right input, I would say it's best to get a stereo RCA cable and run it from the head unit to the amp. Get one long enough to run where the factory wiring goes. Cheap RCA cables are actually fine, but you can spend a few bucks more on whatever the "entry-level" solid cables are from any car stereo product line and they will be slightly better. No need to spend big bucks on "twisted pair" or any gimmick cables - they do nothing.


If the "200W amp" is 200 peak watts and it's only ~100W RMS (or less), you can probably use the factory amp power wire if you can find it and it's 12 gauge. Should be red and attached to the other harness that plugs directly into the amp.

Not sure why you'd want to avoid using RCA cables. They will make the biggest difference in getting the low-distortion signal from the HU to the amp. Spend a few bucks on an RCA cable, zip-tie it along the factory wiring path, plug it in and you are good to go.

You would spend more money and waste more time using RCA Y-adapters and a custom harness trying to get the other end of the factory amp harness to get the signal to the aftermarket amp. Buy an RCA stereo cable and you won't need to buy Y-adapters or mess with the factory wiring to get the signal to the amp. You can just leave the factory wires in there in case you ever put the factory stuff back in.
 






Since the factory HU only has a mono output, and the factory amp only has a mono input, the adapter is probably just a mono plug because whoever designed the harness was assuming that a newer aftermarket head unit with a mono sub output would be used, even though most aftermarket head units still have stereo sub outputs.

You can use a Y-adapter to input the left and right sub outputs from the aftermarket HU into the single sub input of the adapter if you must use the factory amp.

There better be a seperate power wire going to the amp, probably something pretty small like 12-14 gauge.


Even when using a mono amp for a sub, it's not about anything being "in stereo" (which you would need two subs, one on each channel of a two-channel amp for), but it's about the sub getting the sub signals from the left and the right channel. If you just hook up the sub to one channel, just the left or the right, then you only get the bass signals from that channel. If there are bass signals in the other channel, the amp and sub won't receive them or produce them, and it can make the music sound weird.

If you have an aftermarket head unit with a left and right sub/rear output, and a mono amp with a left and right input, I would say it's best to get a stereo RCA cable and run it from the head unit to the amp. Get one long enough to run where the factory wiring goes. Cheap RCA cables are actually fine, but you can spend a few bucks more on whatever the "entry-level" solid cables are from any car stereo product line and they will be slightly better. No need to spend big bucks on "twisted pair" or any gimmick cables - they do nothing.


If the "200W amp" is 200 peak watts and it's only ~100W RMS (or less), you can probably use the factory amp power wire if you can find it and it's 12 gauge. Should be red and attached to the other harness that plugs directly into the amp.

Not sure why you'd want to avoid using RCA cables. They will make the biggest difference in getting the low-distortion signal from the HU to the amp. Spend a few bucks on an RCA cable, zip-tie it along the factory wiring path, plug it in and you are good to go.

You would spend more money and waste more time using RCA Y-adapters and a custom harness trying to get the other end of the factory amp harness to get the signal to the aftermarket amp. Buy an RCA stereo cable and you won't need to buy Y-adapters or mess with the factory wiring to get the signal to the amp. You can just leave the factory wires in there in case you ever put the factory stuff back in.

Thanks for all the info, it clears a lot up. I can run RCAs and am not against it, I was just trying to save myself from doing it if thr existing wiring would work. In my thinking, since there are two wires for audio (pos and neg) already ran, I could use a Y-adapter into those wires creating a single mono cable already ran to the back. Then using another Y-adapter to split that single mono into two monos to run into the amp. I don't care to spend a couple extra dollars if it saves me the work of running wires. Already having power and remote already ran saves half the work.
 






There's no such thing as "positive" or "negative" audio wires. The red channel is for the right side channel, the black channel is for the left side channel.


You could possibly use the included harness and hook the aftermarket HU into the mono harness with a Y-adapter, sticking both channels into one mono channel. But you don't have a harness for the other end, which would plug into the factory amp. The factory amp connector won't plug into the aftermarket amp's RCA inputs, so you need something to go from the factory connector to dual RCA outputs.

If you can find a plug exactly like the input plug on the amp in another adapter kit, you could make connectors up, splicing another Y-adapter cable, soldering it to those connectors, and then you'd have the adapter you need to run a signal through the factory wiring to the amp, but like I said, that would be a lot of work and it would take less time to just buy an RCA cable and plug it in to either end.

Running wires isn't hard. It takes a few seconds to plug in either end, and maybe a few minutes to remove the door sill and stuff the cable in there and maybe use a coat hanger or something to run the cable inside the right side panel. If you're instaling an aftermarket amp, I would guess you have the interior panels off anyway and that should make running the RCA cable a breeze.

On the other hand, making the adapter would take whatever time is needed to seek out the correct plug, get the correct pin connectors, solder them on, plus the cost of the adapter and Y-adapter, which would probably cost you more than the correct length RCA cable.


You may find that Metra or another company actually makes such an adapter for the audio cable, too. Look online or call Crutchfield and ask. If so, then you could just buy that, but I would still say an RCA cable would be best for the money spent, unless maybe you get the other adapter for free.
 






There's no such thing as "positive" or "negative" audio wires. The red channel is for the right side channel, the black channel is for the left side channel.


You could possibly use the included harness and hook the aftermarket HU into the mono harness with a Y-adapter, sticking both channels into one mono channel. But you don't have a harness for the other end, which would plug into the factory amp.

If you can find a plug exactly like the input plug on the amp you could make connectors up, splicing another Y-adapter cable, soldering it to those connectors, and then you'd have the adapter you need to run a signal through the factory wiring to the amp, but like I said, that would be a lot of work and it would take less time to just buy an RCA cable and plug it in to either end.

Running wires isn't hard. It takes a few seconds to plug in either end, and maybe a few minutes to remove the door sill and stuff the cable in there and maybe use a coat hanger or something to run the cable inside the right side panel. If you're instaling an aftermarket amp, I would guess you have the interior panels off anyway and that should make running the RCA cable a breeze.

I'm upgrading the factory amp, and each speaker requires to wires (technically since audio is an AC signal, it's a hot and ground)(in RCAs its a shield and center core, the shield being ground). Maybe an image to describe what I'm wanting to try would help. I know TECHNICALLY it will work, but is it feasible for a quick install...

hDwqVWq.jpg


Since the amp only has a mono output, I don't really need the channels split. Why not just use the factory wires instead of running new ones.

I know it's not a problem to run RCAs, I've done it several times in other vehicles, but why do it if I don't have to? 2 Y-adapters is 5 bucks at my local WalMart, a 12 foot length of RCAs was almost 9. 4 bucks is negligible. But why pay more and do work if it isn't necessary?

I can cut the female end off of one of the Y-adapters and solder it to the existing wiring, and with the harness I'm getting free from crutchfield when I buy my HU I can just plug the Y-adapter on the HU side in.

Thanks again for your information on this. I may actually just try both running RCAs and modifying the factory wiring like I'm trying to describe (not very well, I don't think.. I have a hard time putting what's in my mind into words) just to see if there is a difference in audio quality... I can't think of any reason why it wouldn't work.
 






My suggestion would be to run new wires for everything. If youre already getting an aftermarket head unit I would just run a pair of RCA cables down the passenger side of the car and a power cable down the other. Be sure not to run the power and RCA side by side or your sub will buzz. Grounding is really easy, just drill into the tire well and sand down to bare metal and put a bolt there. The turn on wire can be run with the power wire. I did everything in my 2004 including a second amp and new door speakers and I love the upgrade. The sound difference you would get running new RCA wires would make up my mind, but I know everyone values things differently.

Also, I dont remember there being an actual RCA cable to plug in to behind the radio... I am pretty sure there is just the plug like what would go into the factory head unit so wouldnt you have to run a cable anyways?
 






My suggestion would be to run new wires for everything. If youre already getting an aftermarket head unit I would just run a pair of RCA cables down the passenger side of the car and a power cable down the other. Be sure not to run the power and RCA side by side or your sub will buzz. Grounding is really easy, just drill into the tire well and sand down to bare metal and put a bolt there. The turn on wire can be run with the power wire. I did everything in my 2004 including a second amp and new door speakers and I love the upgrade. The sound difference you would get running new RCA wires would make up my mind, but I know everyone values things differently.

Also, I dont remember there being an actual RCA cable to plug in to behind the radio... I am pretty sure there is just the plug like what would go into the factory head unit so wouldnt you have to run a cable anyways?

In my ride I have a factory amp and sub I'm upgrading, the question is can I just use the factory wiring on that sub, with some customization, and save running new wires.

The power wire and remote wire are already ran and in place from the factory. The stock audio was mono, so my question is more about converting my aftermarket HU's stereo out to mono, putting that into the factory wiring, then splitting that new mono cable at the amp into 2 mono to input to the new amp.

I'm not too sure running RCAs will make a difference in audio, considering the old audio signal was sent with the factory wiring.
 






Are you trying to save time or money?
If time, I'm not sure I see much of a difference, it really doesn't take too long to tuck a couple wires under stuff.
If money I would strongly suggest just waiting until you can get an amp wiring kit.

Judging by what you're saying this isn't what you want to hear but it's only
My opinion. You can definitely do what you're asking if you find the right wires. Are you going to install an rca plug in the back? I am sure the wiring at the factory amp was all just one plug. If you're splitting an rca cable that can be very tricky
 






The wiring illustration you made is correct, as is your summary.

My take is just that it's easier, quicker, cheaper, and better to use RCA cables.


If you want to do the work and solder in the Y-adapter to the amp end, that might work, but keep in mind those thin, tiny factory wires are not going to be as good as a pair of thick, shielded wires in a dedicated stereo RCA cable.

Factory wiring isn't that great, but it doesn't need to be since the amp is low power and the distortion is VERY high - typically 10% or more. Most aftermarket head units output a signal with 0.1 to 1.0% distortion, and most amps are about the same. 1% distortion on a sub is fine, but 10% isn't good, both for the quality of the sound and the longevity of the subwoofer itself. One way of getting noise and distortion into a system is through the cables. Thin, unshielded cables can pick up noise from power, ground, speaker, and signal wires. Those factory cables will pick up noise that a properly shielded stereo RCA cable will not. That's why I think the RCA cable is the better route to go.

If you want to do it just to do it, it will work, but it will not be ideal compared to a stereo RCA cable.

If nothing else, I would call Crutchfield and ask if there is another amp-wire-to-RCA-plug adapter for the other end first, before resorting to cutting the factory wires and see if they will send it out for free, and/or search online to see if such an adapter exists.
 






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