If the wiring is there, be sure to observe proper polarity of the wires. If the speakers are connected out of phase(wired backwards) there will be a lot of sound wave cancellation. In the Benzes, the striped wire in the pair is the +, the plain wire in the pair is the -. Sounds simple, but I have spent hours t-shooting customers cars in the past that had the wires connected improperly. Just thought I would throw that out..