Rick, sounds a a bit like a bad fader but, when you disconnected the fader
you said only the passenger dash speaker quit. Does that mean you had still
had sound on another speaker in the system with the fader pulled???
If you had your meter set to Amps when you measured the door speaker wires,
it is likely you would blow a fuse. (Use 3v AC setting and check for
voltage.). But it also indicates you have a connection back to the amp. Was
it the amp fuse that blew?
Trace the signal (3v AC meter will work OK). Play some music, preferably a
tape with even volume. Set fader to middle. There are many configurations in
MB models and I do not have a wiring diagram for yours so this is just a
guess. Console mounted fader on all my cars are the same though. Here is how
you can test fader signals:
- Most have Left and Right coming out of the radio head unit (or out of a
trunk mounted tuner) into the fader (measure input pins S1 and S2 on fader)
- The S2 (left) input splits into E2 (frt/Left) and A2 (rear/left) (measure
at those pins) You can check fader by watching voltage as you move fader
knob. Voltage will be erratic due to music but you should note a relative
- The S1 (right) input splits into E1 (frt/Right) and A1 (rear/Right)
(measure at those pins)
- If all is OK at fader, note the wire colors at E2, A2, E1,A1, and
measure signals at Amplifier input.
If all that checks out, trace the amp output signals (they naturally will be
a high voltage with the same music and fader setting). Usually the front
dash and front door speakers run off the same amplifier output, so having a
right dash speaker work but not the right front door work is a clue. If
yours is wired that way, you need to trace the wires carefully and check for
bad filter components in the front (caps or coils) in the front speakers.
Also note that some of these cars have a trunk mounted tuner/preamp and
smaller two channel amps mounted behind the seats. That changes the test
procedure a bit.
Thanks for the reply, I think I'm over my head here. All sound, is
off... from all speakers except, the right dash speaker which sounds
like a 10.oo clock radio, flat hand harsh. Unplugging the fader left me
with no sound at all! I sanded the prongs and replugged it, no
improvement at all. The fuse that blew was to the power windows
(right front and left rear) I was thinking I would find a
loose wire or corroded contact. I've got a small multi-meter, and
circuit tester....I was using the multi-meter to test for current in the
door speaker plug when the fuse blew. what is the vacant 3 prongs,
without a plug for?..... on the back of the radio?
I found the trunk mounted amplifier
it has, as I recall a single rectangular 10 pin connector cap plug.
Benz wants 2 hours labor to tell if its good.
Sounds like you are getting close. Good chance that it is a bad fader they
do go out often - subject to coffee and the like. You should either try
testing it with your multi meter as I described or switch it out with a
known good one. The fader is simply a variable resistor which splits the
input signals (e.g. pin S1) into a front signal (e.g. pin E1) and a rear
signal (pin A1). Set your meter to your lowest AC voltage setting, clip one
lead to ground and touch the other leads to pins looking for voltage as
descibed in earlier post. The pins are marked (tiny letters) on the fader
You can also check the fader by pulling it and testing the resistance
between pins S1-E1 and then pins S1-A1. Then pins S2-E2 and then pins
S2-A2. If it is good, resistance will change smoothly as you rotate the
If the fader is good, you will need to get someone on this forum to give you
color codes of the amplifier output wires to test with your meter. Then
you'll know for sure if it is the amp.
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