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Old 06-27-1999, 02:04 PM
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I've installed a new radio, tape and 6 stacker in my 84 300D. I'm currently using the standard wiring setup and everything seems to be working ok. However, I intend to upgrade all four speakers to four and five inch 80w Kenwoods (front and back respectively). I understand that to do so I will need increase the capacity of the wiring (please correct me if I'm wrong).

Do I have to bypass the fade-wheel in the centre consol (the instrument that moderates the level of wattage in the front speakers and the back speakers)or can I use it for the new speakers but simply change the wiring into it?

Also, would I achieve better sound quality by wiring directly from the unit to each of the four speakers?

Finally, is there anything else which might be problematic with this change over?


David Rayment.

1984 300D 235000 kms
Sydney, Australia.
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Old 06-27-1999, 02:24 PM
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When I had a new radio/CD player installed the folks installing bypassed the switch entirely, using the existing wires from the switch to the back and rewiring the front speakers. They told me that to use the switch I'd have to use only 2 of the four outputs on the radio. They also toild me that simply joining the 4 outputs into 2 for the switch to split would be a BAD idea...

How did you do yours?


1982 300D -
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Old 06-27-1999, 03:06 PM
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Hi Nicolas,

Since the new unit is more powerful than the old Becker job, I simply disregarded two of its four power outputs. Connecting only two has been just fine. The trouble is that even with half the power pumping out, and on half volume (a little above normal listening level), the original front speakers begin the crack… From there on it becomes unbearable!

Apart from possibly detracting from the sound quality, did they say why it was bad to let the switch divide up the wattage?

Also, is leaving the switch to govern only two of the four speakers a good idea? I had a feeling it ought to govern all or none... something to do with resistance etc.. but my physics is nothing short of dangerous!

Thanks for your response!


P.S. Frau Thérèse is a very cute car!

1984 300D 235000 kms
Sydney, Australia.
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Old 06-28-1999, 08:45 AM
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Thanks for Frau... :^)

They explained exactly what you were trying to: some resistance thingy. Actually, the switch is not used at all. They ran a new wire and connected it to the wires they removed from the switch. No wires are connected to the switch, which is kind of sad...

I got the scratching sound too. It was related to dried front speakers on my car. Changing the speakers resolved it.

Hoping this helps.

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Old 06-28-1999, 12:08 PM
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Join Date: Mar 1999
Location: Vienna, Virginia, USA
Posts: 36

I did a similar job on a 90 300E. My take at your questions is -- it depends...

First, does your new stereo head unit have a 2 channel amp or 4 channel? Does it have an internal fader control? If it has a fader and/or a 4x amp, I would recommend bypassing the existing console fader entirely. Nicodore is right -- you'd only use half of the radio's power if you used the existing fader, because it splits a 2 channel input to four speakers.

As for the speakers, you should see a HUGE sound improvement by replacing them. The factory originals are only cheap paper cones.

You can use existing wiring if you want. A purist would say that thicker wires are better, and that's generally true, although it might not be worth the effort. Your call. I'd check thickness of the wires (the copper, not the insulation) that come with your new speakers -- if they're not
much thicker that the existing, don't worry about it.

There is a way to use existing 4-speaker MB wiring and bypass the existing fader, if you're willing to cut wires. If your car is like mine, all 4 speaker wire pairs pass right behind the radio location and can be accessed directly.

Hope that helps...
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Old 06-29-1999, 10:18 AM
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Dear PThiringer and Nick,

I've just replaced the front two speakers. The difference in sound quality is substantial! The Kenwood 80w jobs have excellent bass. I'm still using the standard MB wiring... When I buy the rear speakers I'll rewire them all, bypassing the wheel (you're right Nicolas: it is a little sad!).

Thanks for both your advice. I'll be sure to harp back on about this issue if there's any trouble...


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