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Old 04-19-2014, 09:18 PM
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Join Date: Apr 2014
Location: Michigan
Posts: 8
Need help diagnosing stereo issues

Last year I inherited a 1987 300SDL from my grandfather. He had replaced the stock headunit with a Premier DEH-P250. The right front and left speakers work, however there is lots of noise and I don't get anything from either the front/back left speakers. Today, I went and replaced the Premier with a Pioneer X6600BT which went well, but still nothing from the left speakers.

I was under the assumption that there were 2x25 amps located behind the rear seat, so I removed it to find nothing. I then looked for an amp in the passenger side trunk but couldn't find anything without ripping out the carpeting. I tested the left side speakers with a multimeter, and the speakers themselves are fine. When I tested the wiring to the left speakers, nothing.

I've scoured this forum, among others, and haven't found a reliable answer so I could please use some help.

1) Where, if any, are the external power amps located?

2) Considering that I'm not getting any signal to my left side, what is the most likely culprit? A bad connection at the fader?

3) Is there any problem with bypassing the fader, external amps, and just running everything from my new headunit?

4) What's the easiest way to rewire it so everything runs off the headunit? I should be able to find the rear connections at the fader, cut them, and then run them directly to the headunit, right?

Thanks for your help! Also, if anybody has a gray passenger side rear speaker cover, let me know!

Last edited by Lazerboy2000; 04-19-2014 at 11:16 PM.
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Old 04-20-2014, 02:27 PM
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Join Date: Apr 2014
Location: Michigan
Posts: 8
Any help would be greatly appreciated.

I've pulled out the center console and am looking at the fader switch. There are 8 wires connected to the fader.

1. Black/yellow
2. Red/brown
3. Green/black
4. Solid brown
5. Gray/brown
6. Black/white
7. Gray/blue
8. Red/black

Which wires should be cut and which ones are for each speaker?
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Old 04-20-2014, 07:19 PM
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Join Date: Jun 2013
Location: Rochester NY
Posts: 282
1. I'm fairly confident there is no amp. I think that was an early 90's thing.

2. Not quite sure what speakers are or aren't working in your car. You can use a 12v smoke alarm battery to test the speakers individually. If you have the polarity correct the speaker should pop up I believe, if it's reversed it will pop down.

3. No problem at all, I did this. Only the two positive leads go to the fader from the rear speakers. The negatives for the rears and everything else you need should be behind the headunit already. I believe the wires you need from the fader are Red/Brown and Gray/Brown. Again you can use the battery to test this.

4. You shouldn't need to rewire anything, just cut off the fader and pull the wires back to your head unit.
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Old 04-21-2014, 10:05 AM
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Join Date: Apr 2014
Location: Michigan
Posts: 8
Thanks so much!

I just read that MB didn't start using the amps till '88.

Seems strange that only the positive leads go to the fader but hopefully that explains my problem. I'll go ahead and cut off the fader and test the leads with a battery.
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