By OEM2, I assume you are referring to the PAC OEM2 line output converter? With 4volt pre-amp output, this should not be necessary, and may be bringing the 4volt output to a line level signal.

 

Thanks! So that will cause the weak rear deck? What can I do now? Just connect the head unit directly to the harness plugged out from the previous OE radio? Any idea of how to connect to the 4v pre-amp output on the kenwood?

 

The Metra 70-1786 harness adaptor is one that most use. It plugs into the connectors you remove from the stock radio and provides power, ground, etc and two sets of RCA connectors to connect to your new HU. Sorry if I missed it earlier, I thought you had one of these.

If you have a Fry's close by, they usually stock this adaptor. If not, they are easy to find online.

Metra 70-1786 (met-701786) Amplifier Integration Harness for

 

What I used was Metra 70-1784 as used by many people.
Amazon.com: Metra 70-1784 Radio Wiring Harness for Audi 88-99/Volkswagen 80-Up: Car Electronics

This is the thread I followed.
W210 Aftermarket HU with Bose - MBWorld.org Forums

Would Metra 70-1786 make a difference in terms of rear deck? Then I would get one and have it connected. And after that there would be no use of OEM2 I guess?

 

I would recommend just going with the Metra 70-1786 to save yourself time and money. With the 70-1784, how are you connecting the "speaker" wires from the harness? If you connect them to the receiver speaker output, you would need to insert a line adapter to attenuate the speaker voltage coming from the receiver. If you connect them to the pre-amp out on the receiver, you would need to solder RCA jacks. Either option is more costly and time consuming than just getting the 70-1786 harness.

Regarding the rear deck bass sound, you may want to play with the receiver settings to isolate possible cause. Put all the sound into the rear speakers, and select an appropriate equalizer setting. Is the sound level weak, or is the quality of the sound poor? If sound level is weak, that may have to do with the Bose amp input that that you are feeding from the receiver. I have a Pioneer BT7000 receiver and get pretty loud sound by going to "45" volume on the receiver (I think it goes up to 100, but never tried it that high). If the bass sound quality is poor, it may have to do with the bass response of the speaker and/or the bose amp. I plan to add a subwoofer to my installation. You could consider this as well--cost is $150 to $200, and you can get a complete amp/subwoofer enclosure to make things simple, if you want.

 

I have 70-1784 connected already and it works so not a problem for me for the connection, the problem is that the subwoofer in the rear deck is not as strong as before and I don't know is because I didn't use the 4v pre-amp.

The speakers on the rear door sounds normal actually, only the subwoofers are weak. I guess both rear door speaker and rear deck subwoofers are using (sharing) the rear left and rear right output from the head unit (gray and violet wires), how come the rear door is loud while the subwoofer is weak? When I adjust the setting on the head unit I can get extreme loud sound from the rear door speaker but still weak base from the subwoofers...

 

Well, the harness might work, but the Bose amp is expecting line-level input (which is why the 4v pre-amp output is important). So I'm wondering how it might be connected. From what you've said (and linked to), it looks like you may have used the 70-1784 to connect power, etc. and the OEM-2 to connect the new HU to the amplifier, no?

If you look at the PDF here;
http://www.pac-audio.com/pacproductdata/oem-2/1_instructions/oem-2_instructions_061107.pdf

... you can see that the OEM-2 adapter is also converting speaker level/line level inputs. The cleanest sound comes from using line-level between the HU and Amp.

Interesting note in the PDF above, I believe it may apply to the Mercedes design as well, as it makes sense.

"Some Chrysler/Dodge vehicles with a Infinity premium sound system do not
need any interface. If the speakers fade and balance correctly with this
interface installed, but you have very little volume, then you do not need this
interface."

 

Yes you are right, the only thing is that the OEM2 was connected to the Amp through 70-1784 harness also.

I guess the question is why only the subwoofers are weaker? This rear deck speakers share the output with the rear door speakers but rear door speakers can be very loud while the subwoofers are still weak.... The kenwood has a specific setting for subwoofer and it has no effect on the rear deck speakers as far as I can tell...

 

I would check something very simple first, are both rear deck speakers wired properly, in particular the earth!

 

From what I've read so far, your factory installed radio was working properly (good sound, not great), right?

And now that you've upgraded your HU, the sound is lacking low end?

I believe using the Metra 70-1786 harness adapter will help improve the sound considerably. I did find the wiring diagrams on the MBWorld forums, if you are interested, but I think you really will be set if you run the line-level signal from the new HU using the adapter above.

MBWorld.org Forums - View Single Post - W210 speaker wiring diagram

 

The factory installed radio does not have a CD changer connected so I only listened to the tuner several times. However my previous E320 with CD changer produce much better sound comparing to this new kenwood unit, which have the same bose speaker system. I guess this is b/c of the powerful and deep bass comes from the rear deck which is lacking on this one. So I assume that some setting is not correct for the input to the rear deck speakers... I probably will try to use the 70-1786 4v output to see if the rear deck can get more powerful output.

 

Check speaker connections to assure that they are phased correctly. An out of phase speaker can degrade (cancel) bass response (loudness).