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).