low-level output on stock system

[Brian-bmw]

Originally Posted by DouglasABaker

So there are no systems that have just a head unit without the additional radio box in the trunk?

That is interesting only because I helped someone (via phone) with an install who said he only had a head unit w/ no box in the back...

d-

At a high level, there are probably 6 major permutations of the audio system:

1) In-dash radio with no amplifier (6 speaker)
2) In-dash radio with standard HiFi amp (10 speaker)
3) In-dash radio with Top HiFi DSP amp (12 or 14 speaker)
4) Navigation with trunk radio and no amplifier (6 speaker)
5) Navigation with trunk radio and standard HiFi amp (10 speaker)
6) Navigation with trunk radio and Top HiFi DSP amp (12 or 14 speaker)

The first three perrmutations have the radio in the dash. It is the component with the tape or CD player. The last three permutations have the board monitor screen up front and the separate radio module in the trunk.

My hunch is that the install you helped with must have been system #1. That would have the standard radio with MID in the dash and no separate external amplifier. In that setup, the speakers are powered directly by the radio module. It is analogous to permutation #4, but in that case the radio module is in the trunk with no external amp, and the speakers feed directly to the trunk radio.

The other point to note about the above is that the same radio module part functions for scenarios #1, #2, #3. And, the same trunk radio supports scenarios #4, #5, and #6. The radio scans the I-Bus for which amp (if any is installed) and then decides out it should change its output.