You'll need to have the DSP system to fully install the OEM subwoofer. The cable you're finding is likely the pre-wired loom for the rear PDC sensors. I purchased the OEM subwoofer for my non-DSP system a few years ago with a plan to bridge it as an extra bass speaker but I ended up upgrading to the full DSP system. That was way too much of an endeavor and if I had to do it over again I would had left it alone. But im happy with the results. You should consider adding the Sub as in the above post.

One of the reasons I upgraded was that DSP was an 8 Ohm system with a higher output amp and my existing Hi-Fi was 2 Ohm. The OE Sub and the DSP door speakers are 8 Ohm. The DSP main door speakers are also a full-range design (the Hi-Fi are full woofers). Since the OE subwoofer handles all the low frequencies the sound from the doors and dash is much richer. Granted the OE sub doesn't thump spectacularly but it really isn't supposed to, only that the lowest frequencies are instead routed to it for added depth.

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2001 3.0i * SOLD *
Current
2010 E83 Alpine White