I just installed the Alpine CDA-9835 deck and MRD-M301 amp in my '99 Passat using a wiring harness. I tapped the remote lead from the amp into to REMOTE of the wiring harness. My problem is that my amp is ALWAYS on, regardless of whether the stereo is on or off I tried tapping into the P. Ant wire with the exact same results.
On almost every car the remote wire from the harness is a constant power suppy, usually becuase the deck has a clock. But in your case your using a After market deck. You may need to tap the remote in to some where else (another wire). Look on your diagram for the instructions. I know my deck has a seperate AMP remote coming out of the harness. If you have no luck then you may want to re-locate the remote to a fuse box. Use the ACC, or IGN, to tap into those fuses.