[Speed Racer]

I just got off the phone and checked with a local car stereo dealer that handles Metra accessories. The wiring harness adapter for our cars is still available, and they had a few in stock.

Here's some text straight out of the CelicaSupra.com FAQ section:
http://www.celicasupra.com/stereoopt.htm

1. Wiring Harness
I highly recommend using a METRA wiring harness (part #70-1398). With this harness you will not have to cut and ruin the clean Toyota wiring. The harness should cost around $10 USD, a small fee for a much cleaner, and easier install.

There's no reason to hack the plugs off the wiring harness and make a mess of things in your console, when you can buy one of these and then wire it to your stereo.