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1995 E320 Wagon and 1991 300CE Coupe
1 Posts
Discussion Starter · #1 ·

Car in question is my 1991 300CE, specifically working on some stereo shenanigans. Background is that PO installed an aftermarket headunit and there is currently only sound coming from the front dash RH speaker, full stop. I had nothing to do with the removal/install of the HU, so I am just inheriting and investigating from now.

This is what happens when controls (HU and fader) are operated:

Fader switch
center position sound remains at front RH only
forward position sound remains at front RH only
rear position ZERO sound

Head unit
Balance LEFT position with ZERO sound--RIGHT position front RH speaker only
Fader FRONT position with front RH speaker only--REAR position with zero sound

Basically, I have tried practically all combinations of fader and HU controls and the result is either only sound from front dash RH speaker or ZERO sound. It seems to me that both the HU controls and fader both have an effect on the sound output. However I am at a loss as to why there is only sound coming from the front RH speaker.

I have done some of my own forensic investigation and have removed and looked at some basic items (head unit, fader switch etc.) and nothing seems to be jumping out at me as a culprit. Appears to be a fairly tidy job with the HU wiring installation job (an aftermarket harness used with the original MB plug) and the front speaker two-prong connections solid as well. I have completely disconnected the fader and taken it out of the equation entirely, but this also has no effect from the above mentioned sound results. I also looked at the female portion of the fader switch and it appears to be unmolested as delivered from factory.

This vehicle has front dash speakers, door (bass) speakers and rear parcel shelf speakers and (I believe) amps located on passenger side of trunk. All of these items appear to be unmolested and stock.

Is there something obvious that I am missing to check? What do you Clouseau types recommend me to do as next steps? Are there more permutations of my sound check experiment that need to be tested with results reported? I am planning on installing a new bluetooth HU, but not sure if the original HU is the source of this sound issue or not. There are no other modifications that are planned on my part outside of a fresh HU install job.

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· Registered
300te 4Matic, 1992, 225,000 miles. W447 Vito Sport Long 116cdi, 2018, 70,000 miles.
703 Posts
As an insight to the original system.
The amp in the back is the heart of the system and effectively supplied the whole original Becker system. The original Becker head unit was just a display, and tuner and was connected to the amp via a multi strand DIN cable, so I doubt an after market head unit will be compatible. All of the speaker cables and fader come from the amp!
Hope this helps
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