# Gm loop back harness



## fedwells (Jul 9, 2019)

Is there anyone here that could tell me how to make a loop back harness for a 2015 gmc Sierra double non Bose? I have the two metra 71-2107 & 70-2057 connectors


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## Jg144 (Mar 14, 2017)

Not sure about making new . But they sell them ready to go
https://lljcustoms.com


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## JH1973 (Apr 21, 2017)

You'll only need the green connectors(male and female) in your Metra kits.Pull the green connector out of your stock radio,you'll need to know the wire functions which I'll provide below.

The first thing you'll need to do is connect the power and ground wires together from the male to the female Metra harness.As you look at your stock radio connector,the power is red/violet and the ground is black.That way you know which wire in the Metra harness is power and ground(not sure if the wire colors match from Metra harness to stock radio connector).Then from the male metra connector run your speaker outputs into your line converter or high level inputs of your amp.Then run all of your speaker outputs from the new amplifier into the female metra connector.Lastly,just plug the stock male connector into the female metra connector and the male metra connector into the stock radio.........done!

In case the metra wire colors don't match here is the chart for that stock green connector......
12v.........red/violet
ground........black
fr left +......blue
fr left - .......brown/blue
fr right + .....yellow
fr right - ......yellow/black
rear left + ......green
rear left - .......green/black
rear right + ......white
rear right - .......blue/black

You may need to move pins around in the harness if the slots you need are empty.Use something very skinny and rigid like a tiny flathead to lift the plastic tabs and pull the wires out from the back.

If this is too confusing then you can mail me those metra connectors and I'll build it for you......for some $$ of course.....


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## fedwells (Jul 9, 2019)

Haven’t tried it yet but how much would you charge to make the harness?


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## JH1973 (Apr 21, 2017)

fedwells said:


> Haven’t tried it yet but how much would you charge to make the harness?


 $6 per foot to cover wire costs and OEM tesa tape.So however long you want the wires to be from stock radio to line converter and amplifier.

And of course I will support you along the way until your install is done.Won't leave you in the dark.


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## fedwells (Jul 9, 2019)

I purchased 20foot of 9 wire and 2 rolls of Tesa tape with the meta kit


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## JH1973 (Apr 21, 2017)

fedwells said:


> I purchased 20foot of 9 wire and 2 rolls of Tesa tape with the meta kit


In that case just mail all the stuff to me and I'll build it for $35.That will include shipping back to you.Email me at [email protected] if you're interested.


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## Lupemartinez (Jan 22, 2020)

fedwells said:


> Is there anyone here that could tell me how to make a loop back harness for a 2015 gmc Sierra double non Bose? I have the two metra 71-2107 & 70-2057 connectors


Where did you buy the kit of connectors?


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## Cstrife2 (May 27, 2009)

Jg144 said:


> Not sure about making new . But they sell them ready to go
> https://lljcustoms.com


DO NOT do business with these guys.... I can go into detail about my experience with them just trying to buy a harness for my car, however a quick look around the forums will show some other user experiences with them that align with the issues I had.


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## drawk (Apr 8, 2020)

JH1973 said:


> You'll only need the green connectors(male and female) in your Metra kits.Pull the green connector out of your stock radio,you'll need to know the wire functions which I'll provide below.
> 
> The first thing you'll need to do is connect the power and ground wires together from the male to the female Metra harness.As you look at your stock radio connector,the power is red/violet and the ground is black.That way you know which wire in the Metra harness is power and ground(not sure if the wire colors match from Metra harness to stock radio connector).Then from the male metra connector run your speaker outputs into your line converter or high level inputs of your amp.Then run all of your speaker outputs from the new amplifier into the female metra connector.Lastly,just plug the stock male connector into the female metra connector and the male metra connector into the stock radio.........done!
> 
> ...


Do you know the exact pins in which each wire should go?


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## drawk (Apr 8, 2020)

drawk said:


> Do you know the exact pins in which each wire should go?


T


JH1973 said:


> You'll only need the green connectors(male and female) in your Metra kits.Pull the green connector out of your stock radio,you'll need to know the wire functions which I'll provide below.
> 
> The first thing you'll need to do is connect the power and ground wires together from the male to the female Metra harness.As you look at your stock radio connector,the power is red/violet and the ground is black.That way you know which wire in the Metra harness is power and ground(not sure if the wire colors match from Metra harness to stock radio connector).Then from the male metra connector run your speaker outputs into your line converter or high level inputs of your amp.Then run all of your speaker outputs from the new amplifier into the female metra connector.Lastly,just plug the stock male connector into the female metra connector and the male metra connector into the stock radio.........done!
> 
> ...


Is this the same even for a two channel amp? I've seen the plug and play harness which I am trying to replicate. Just not sure what to do with the rear speaker wires as I am only running the front speaker wires to the LP72 pac.


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## ajt976 (Feb 27, 2019)

drawk said:


> Is this the same even for a two channel amp? I've seen the plug and play harness which I am trying to replicate. Just not sure what to do with the rear speaker wires as I am only running the front speaker wires to the LP72 pac.


You can depin the connector to only retain the front outputs if you wish. It's kind of a pain in the but but with a little patience can be done. I actually removed all of the OEM signal outputs from the radio side (using the PAC AmpPro for signal) but fed everything back into the vehicle side so I could use the OEM wiring.

All that said, I might be inclined to leave the harness as is and leave the other speaker outputs there in case you decide to upgrade later on. If memory serves me right, I believe the chimes and phone audio comes from one or both of the front speakers. Would be nice to have options down the line if you wanted to use or lose those chimes depending on how you are setup.


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## drawk (Apr 8, 2020)

ajt976 said:


> You can depin the connector to only retain the front outputs if you wish. It's kind of a pain in the but but with a little patience can be done. I actually removed all of the OEM signal outputs from the radio side (using the PAC AmpPro for signal) but fed everything back into the vehicle side so I could use the OEM wiring.
> 
> All that said, I might be inclined to leave the harness as is and leave the other speaker outputs there in case you decide to upgrade later on. If memory serves me right, I believe the chimes and phone audio comes from one or both of the front speakers. Would be nice to have options down the line if you wanted to use or lose those chimes depending on how you are setup.


If I de-pin the rear speakers, will I lose function of them entirely?


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## ajt976 (Feb 27, 2019)

Short answer is yes, removing those pins will mean your rear speakers will no longer be powered by the OEM radio.

I guess it depends on what your plans are. If you intend to run speakers off the OEM head unit AND from an amplifier fed by the PAC unit, you need to retain them. If you plan on using an amplifier to power all speakers going forward, then you may not. It would depend on what you wanted to use for signal (front vs rear) to wire up the LP72.

What is your setup?


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## drawk (Apr 8, 2020)

ajt976 said:


> Short answer is yes, removing those pins will mean your rear speakers will no longer be powered by the OEM radio.
> 
> I guess it depends on what your plans are. If you intend to run speakers off the OEM head unit AND from an amplifier fed by the PAC unit, you need to retain them. If you plan on using an amplifier to power all speakers going forward, then you may not. It would depend on what you wanted to use for signal (front vs rear) to wire up the LP72.
> 
> What is your setup?


Yes, I would like to run the front speakers from my my amp, and then maintain the rear speakers from the head unit. The front speakers will be going to the LP7-2. I guess I am getting confused on which wires to connect and to where. Here is what I have done thus far. Don't know if it is right. But this is where I am at.


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## ajt976 (Feb 27, 2019)

Okay so here's a shot when I was figuring out what pins I needed on the two connectors I used. My guess is that you need to finish wiring up your LOC to the front right/left, then you would need to wire together the rear right/left to the other side of the harness so you could continue feeding that into the OEM wiring to get power to your rear speakers.









You might test the connection to the rear speakers just to be sure which ones on the female side of the harness you need to be sending that in to.


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## drawk (Apr 8, 2020)

ajt976 said:


> Okay so here's a shot when I was figuring out what pins I needed on the two connectors I used. My guess is that you need to finish wiring up your LOC to the front right/left, then you would need to wire together the rear right/left to the other side of the harness so you could continue feeding that into the OEM wiring to get power to your rear speakers.
> View attachment 267240
> 
> 
> You might test the connection to the rear speakers just to be sure which ones on the female side of the harness you need to be sending that in to.


Awesome that sounds good. And just to make sure, I want the LOC attaching from the male metra harness, not the female correct? I had seen in a video they had it connected to the female side... But on here they said connect it to the male. The only thing they had connected in the video was the power between the harnesses.


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## ajt976 (Feb 27, 2019)

Yea, the male side is what plugs into the radio, that's where you'd need to get the signal from:









Note - In my case, I removed all of those because I wasn't using any signal from the stock radio after I installed the AmpPro, that's why you only see the black and yellow power wires on the male side of my harness.


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## drawk (Apr 8, 2020)

Awesome, I'll give it a shot and see how it turns out. Thanks for all of the help!


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## drawk (Apr 8, 2020)

ajt976 said:


> Yea, the male side is what plugs into the radio, that's where you'd need to get the signal from:
> View attachment 267242
> 
> 
> Note - In my case, I removed all of those because I wasn't using any signal from the stock radio after I installed the AmpPro, that's why you only see the black and yellow power wires on the male side of my harness.


I plugged the harness in today just to test it out, and make sure I was getting power to my LOC. Everything worked out, had sound to the rear speakers, and nothing to the front, as I haven't run my amplifier wires yet. Did you lose the sound of your door chime? and do you know if it will affect anything else like calling/ hands free talking while driving? Now that I just thought about it, it could have been because there was nothing coming out of the front speakers.


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## ajt976 (Feb 27, 2019)

drawk said:


> I plugged the harness in today just to test it out, and make sure I was getting power to my LOC. Everything worked out, had sound to the rear speakers, and nothing to the front, as I haven't run my amplifier wires yet. Did you lose the sound of your door chime? and do you know if it will affect anything else like calling/ hands free talking while driving? Now that I just thought about it, it could have been because there was nothing coming out of the front speakers.


Yea, so the chimes and phone audio will come out of the front speakers, you won't have those until you get your amp and front speakers hooked up.

Also realize that your chimes will then be amplified and likely louder than stock, it's something that others have run into when using the OEM signal to feed an LOC.


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