You'll need a 'premium' amp bypass harness. Crutchfield has proved to be the most reliable source for the correct harness connectors for the Contour, but Circuit City and Best Buy sometimes provide the right stuff too.

1999 Contour SE Sport MTX75 T-Red/Grey
Audio: Pioneer DEH-7400MP (MP3 CD), Pioneer TS-A6857 front & rear, PPI PCX-250, Infinity Perfect 10.1
Other: cup holders, cargo net, Blizzaks, Potenza RE950s