I didnt realize you have the single amp system. Most 93 124's have a dual amp system and the plugs are reverseable. This amp just runs the door speakers and the radio power runs two channel through it and then to the fader control and 4 ch out of fader to the front and rear speakers. If you don't have a problem with the rear right also Iwould have to say the problem is in the speaker or connection.

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The Mercedes Specialists Since 1986