2008 Sub Install using factory wiring and Sync Headunit(non-Sub) - Focus Fanatics
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Old 12-24-2013, 11:35 PM   #1
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2008 Sub Install using factory wiring and Sync Headunit(non-Sub)

Merry Christmas to all,

I have been toying with the idea of putting a subwoofer in my Sync equipped SES and have been considering many options. I have considered a LOC but after tearing out the panels in my trunk I have come up with a different plan of action. I have found the factory sub connection and have tested the pins. My vehicle has the sub fuse in main box and the constant 12V line on the plug is hot. When I test the Amp enable pins or audio pins however I get nothing. I am going to take a look behind my dash tomorrow and see if there is a plug at the other end of the harness that is not connected to the OEM H/U. If anyone has any info regarding the turn on method for the factory amp(i.e. CAN switched or standard 12V+ switched) please let me know. I figure I will use this thread as a log for others if nothing else.

Link to pinout on Autozones website:


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Old 12-25-2013, 07:30 AM   #2
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can switched I believe
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Old 12-25-2013, 06:50 PM   #3
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I've been toying with the idea of putting a sub in my trunk for awhile. Keep us informed as to how this goes!
Roush performance intake, Exedy 12.5 lb flywheel, Massive 76A lower engine mount... more to come with more money.
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Old 12-26-2013, 01:48 AM   #4
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Moved to "Car Audio, SYNC, MyFord Touch & Electronics". You might get better help here since most of these people in this section have done this already.
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Old 01-14-2014, 07:03 AM   #5
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Sorry for not getting back here quickly. I've been busy with the new semester. Also thanks for moving the thread I did not notice that section when I was looking for a place to post this. Anyway I finally got around to pulling my dash apart using the instructions from this thread http://www.focusfanatics.com/forum/showthread.php?t=147694. Unfortunately I did not find what I was looking for. I assumed the Subwoofer output was a locked feature of the head-unit and it was just not enabled/plugged in. Well, turns out my head-unit doesn't have the plug so I guess its only available on the ones that came with the sub from the factory. I would assume if you managed to acquire one of those head units you could use the stock connection with either the factory or an aftermarket sub. From what I seen in diagrams the stock sub connector in the trunk is low level pre out coming from the stock head unit, so for those that have the stock system with the sub you should be able to just tap into that plug for the mono pre-out and possibly the remote line. Since I do not have the output on my head unit I am unable to test if the amp enable line is can or just 12V switched but if anyone wants to go down this road just test it with a multimeter or testlight the pinout for the plug in the trunk is in my first post.

With this matter settled I see 3 options for adding a sub in my trunk: Find a stock radio that has the pre-out and see if it works, buy a PAC low level converter, or look into one of those Kenwood head units that you can integrate with sync. The cheapest option at this time seems to be the PAC and is most likely what I am going to go with. Down the road I might look into one of those compatible Kenwoods and the associated idatalink maestro Sync interface module.

Something I did find during this adenture that worked and I mentioned in my original post is the fact that the 20A Sub fuse is installed in my focus and the line is hot. I have set it up to charge my maglite I mounted in the trunk but plan to cut a hole in the interior carpet/fiberglass stuff on the left side of the trunk and install a 12V socket for easy access in the trunk.

Anyway, enough of my blabbering, time for pictures :)

Got the dash apart in this picture.

Back of the radio, As you can see I am missing the third connector where the sub harness plugs in.

Another picture of the back of the radio. It is REALLY tight back there if you don't unplug everything.

Here is the diagram for the plug that goes to the back of the headunit

The diagram for the plug that sits in the trunk (Linked in the original post)

and the schematic for the sub system

courtesy of Autozone.

Edit: I forgot to add, if anyone in the Sync section sees an error in any of my assumptions please feel free to correct me. As things like the turn on wire and pre-out are assumptions that I have made from looking at the diagrams. Due to my lack of the stock connection I am unable to definitively test anything.


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Old 01-14-2014, 08:43 AM   #6
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I got this from the workshop manual.

The sub woofer amplifier receives voltage through circuit SBP38 (BN/RD) and ground through circuit GD161 (BK/YE). To enable the subwoofer amplifier, the audio control module (ACM) sends voltage through the enable/clip circuit SME23 (VT/RD). The circuit acts as both an output (to enable the amplifier) and an input (to detect an amplifier overload condition). A variable resistor in the subwoofer amplifier modifies the voltage signal from the ACM. In the event of an overload, the ACM clips the audio output signal to the amplifier (heard as distortion), in order to prevent damage to the amplifier and speakers.

The clip/enable status is based on the following voltages, as detected by the ACM:

Less than 0.4 volts: amplifier disabled
Between 3.8 and 6.7 volts: amplifier enabled
Greater than 8.5 volts: amplifier clipped

So you would need to find an Audiophile factory radio as it would be configured for the sub woofer and have the connector on the back. Or you could simply create your own clip/ enable circuit using resistors and connect in a factory sub/ amp combo.
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Old 02-01-2014, 11:38 AM   #7
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Used the PAC AOEM-FRD24, mounted it near the passenger's left foot partially concealed by the center console side plastic (under the dash), stuffed (and zipped) the extra cable in a small open area nearby, ran the rest of the wiring under the rug and sill to where I installed the small sub under the passenger's seat. Pics of the PAC install on request. Maybe.

No splicing, install of the PAC used only duct tape, electrical tape, and zip ties.

Protip - don't 'test' the harness plugs on the PAC by plugging them in to each other. It took me an embarrassing amount of time to separate them.
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