So I finally decided to install an after market stereo in my 84 300D, PO had removed the stock and install an after market. but the fader wheel on the center counsel was not wire properly. Hence rear speaker did not sound good.

How do I connect all the speaker wires from the after market stereo with four sets of wires to the two sets of wires for the stock stereo with the fader on the counsel functioning.

Right now just to have sound, I have the front speaker wires from the after market stereo connected to the two sets of wires. the rear speaker are getting something but not as good as the front. None of the rear speaker wires from the after market stereo are connected.

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1984 300D, 1972 LT1 Corvette, 2014 Artic White 3LT/Z51 C7, 2013 650i Convertible BMW, 1994 Kawasaki Vulcan, 1992 Yamaha Seca II and 1996 Dodge Ram 2500.

You will need to connect two of the the outputs from the head unit directly to the fader. The fader should then take those two and output four.

The rear outputs on the head unit are left disconnected.

Typically folks bypass the fader as they go bad, get dirty etc.

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Most new stereos have 4 amps. The fader is meant for a 2 amp system.

In an old 123/124/126 with the fader you have to bypass it completely and get all 8 speaker wires isolated and connected to the head unit's outputs.

It's not too hard to follow the wire pack from the radio to the fader to the speakers.
Or just run all new wires.

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both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

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1987 300TD sold to vstech