The issue is that the fader gets two-channel input (only two wires), and
outputs four-channels (only four wires).  The _ground_ or _negative_ signal
to the speakers doesn't go through the fader, it goes from the radio
through connector X48H and X48G, which are not listed in the FSM index of
connector locations.  I suspect they are somewhere under the center
console.  So I would need to run two more wires to that fader socket for
either the front or the rear speakers, OR I could go directly to the front
speakers from the radio (those connectors are readily available right
behind the radio hole), and then jumper the fader input wires to the rear
speaker signals.  Unfortunately the electrical diagram from the FSM does
not give pin numbers at the fader socket, so I guess that will be trial and
error with a 9v battery.

I'm concerned because I've read in several forum posts that modern radios
don't like how Mercedes grounded the speakers in the 80's, now I need to
see how the Becker 1492 installation compares to my 87 wagon, maybe in
'94/'95 Mercedes continued with its speaker grounding method and the 1492
won't care.

I'd like to put the Aux Input plug in the hole for the fader.

Charleston SC

On Fri, Jun 19, 2015 at 9:44 AM, Rich Thomas via Mercedes <> wrote:

> You could just clip a jumper across the terminals for each side and turn
> the fader "off" -- that will create the easy path for the electrons to
> flow.  Won't bugger the switch.
> --R
> On 6/19/15 9:26 AM, Meade Dillon via Mercedes wrote:
>> Thanks Rich.  I think the easy route will be to bypass the fader, I'd like
>> to figure out how to do that without cutting off the fader connector so
>> that it can be restored to stock in the future.  I'm not having much luck
>> finding a DIY on the intertubes for which pins to jumper (or run new wires
>> to) in order to route sound signal to the rear speakers.
>> Aux input: yes, it looks like hacking into the cassette board will be the
>> best option, if I can't figure out how to use the CD changer inputs.  I'm
>> not sure how to approach that yet, may need an o-scope to sample the
>> signals.
>> -------------
>> Max
>> Charleston SC
>> On Fri, Jun 19, 2015 at 9:20 AM, Rich Thomas via Mercedes <
>>> wrote:
>>  I think those fader "swithces" are just variable resistors/potentiometer
>>> things. put a meter on it and see what it does.
>>> Newer head units (I don't mean Beckers -- no idea what they have -- but
>>> any other thing you buy) have the fader built in so you can just bypass
>>> it
>>> and use the "native" function.
>>> Again, I don't know about Beckers but I was looking at the schematic for
>>> the radio in my truck, which I liberated from the 2000 Suburban when I
>>> put
>>> a new unit in there.  I want to put an aux input for an ipod or a
>>> bluetooth
>>> module, and the way to do that is to tap into the cassette line.  The
>>> unit
>>> itself has a remote cassette player that uses that line so just a matter
>>> of
>>> putting the wires and a mini-plug socket somewhere near the unit.  Of
>>> course this is on my "to-do" list...  Some people have found success by
>>> just opening up the unit and looking at the board or inputs and just
>>> tapping/splicing into the proper wire or trace or plug or something on
>>> the
>>> main board -- apparently most of them are annotated on the boards or it
>>> is
>>> easy enough to see what goes where.
>>> --R
>>>  _______________________________________
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