How To: Access The Factory Amplifier

[djjasond]

Background: I created these instructions and captured these pictures to help those who would like to keep their factory head unit and steering wheel controls but add after market amplifiers. There are no rca plugs or “outs” on the rear of the factory head unit. Unless your aftermarket amplifier has line level inputs, you must use a line output converter to provide signal to those amps. (Note: A qualified installer may have other tricks to accomplish this but the common person would use a line output converter.) The cleanest signal for your line output converter comes from the factory head unit before the factory amplifier. The best place to intercept this source signal is at the factory amplifier. The following instructions will help you gain access to the factory amplifier and necessary wires for your line output converter.

Line Output Converters (LOC): There are many, many LOC’s out there and even more opinions about them. Every shop and installer has their favorites. Please search the forum for “line output converter” or “LOC” for more information. General advice would be that the signal from the factory deck is very clean and does not require the high-end models with the fancy eq’ing and calibration features. The signal processing happens in the factory amplifier. If you add a LOC off the rear speaker inputs, after the factory amp, you may consider a more advanced LOC but several members have had good luck with standard LOC’s. Again, it is the subject of great debate so I recommend you do your own research.

UConnect: If you want to keep UConnect working through your dash speakers and powered by the factory amp, STOP here! You must tap the signal for your line output converter off the rear speakers in the trunk. Tapping the signal prior to the factory amp disables all factory speakers!

Disclaimer: This was a true Do It Yourself pictorial and as such may not be 100% technically accurate. The pictures are of a 2006 300C with Sound Group II. Other years and models may have slight differences. I expect follow up posts from the loyal members of this site with corrections as needed. The instructions also assume a basic understanding of car audio and the 300C’s audio options. Please be sure to read the Audio FAQ before posting any questions to this thread. (FAQ - Audio Upgrades).

[djjasond]

How to access the factory amplifier:

1) Disconnect the negative battery terminal using a 10mm socket. Battery is in the trunk next to the spare tire. (picture 01). Once the battery is disconnected, do not close the trunk or you will be forced to crawl through your backseat into the trunk and pull the emergency release handle. This is about as fun as touching your toes after Thanksgiving dinner. I recommend taping the latch so that “helpful” friends and relatives are unable to close the trunk in your absence. Remove the trim panel to the left of the headlight switch by gently tugging on the top of the panel. The panel is held in place by two clips. (picture 02, 03)

[djjasond]

2) Remove the knee panel under the steering wheel that is held in place by two screws (use Phillips head screwdriver or 7mm socket) and several clips. After removing the screws, gently tug on the panel to release the clips and gain access to the back of the panel. (Note: There is an electrical plug connected to the trunk release button that is easily disconnected. The panel is also connected to the parking brake cable that is not easily disconnected. I was able to leave it connected to the panel and rotate the panel out of the way with plenty of room to access the amp.) (picture 04,05,06,07)

[djjasond]

3) Remove the metal panel directly below the steering column that is held in place by four 10mm bolts (picture 08). (Note: Pro installers – there is a ton of room behind this panel for possibly an 8”-10” subwoofer, stash box, etc.) Then remove the insulation panel that is held in place by two plastic rivets (use trim panel removal tool or similar pry bar). (picture 09,10)

[djjasond]

4) You now have access to the bottom of the amplifier where the wiring harnesses are connected. There are two plugs. The input signal from the factory head unit is on the rear and larger plug. Pictures show the rear plug unplugged and wires tapped. Use the following wires for your line output converter:
Radio pin A18- Radio Left +: Dark Green / DarkBlue (amp pin A7)
Radio pin A19- Radio Left - : Dark Green / Orange (amp pin A19)
Radio pin A21- Radio Right +: Grey / Dark Blue (amp pin A8 )
Radio pin A20- Radio Right -: Grey / Orange (amp pin A19)
(picture 11, 12)

[djjasond]

5) Optional step – remove the trim panel along the bottom of the door. You typically would run your speaker wires to aftermarket amps in the trunk under this panel and the one just like it in the rear doorframe. Many line output converters require power. You may wish to run the signal wires and install your LOC in the trunk since the battery is located there. You can move the trim panel at the base of the rear seat, without removing the rear seat, just enough to tuck the wires under it. (picture 13,14)

[djjasond]

Look for similar posts on removing door panels and the rear deck in the near future. Enjoy!

[HaTaX]

Awesome, just awesome.....

Thanks for the great write up with the pictures, should give ALOT of people a good starting place for where to get the signals.

Looking forward to something similar for the front door speakers.

[HEMMISSEY]

about time someone actually took pic's of this! Thanks a million.. Mods this should be a sticky... thanks for the write up djjasond

[rogue]

djjasond thanks so much for making this post. I never documented my installs with photos as great as yours.

Excellent!