The amp should have a high level or speaker level input. It will come with a plug that plugs into it with speaker wire sized color coded wires protruding from it. You need to wire them to the corresponding wires coming out of the back of the stock stereo that go to the speakers. The installation instructions that come with the amp will tell you exactly how to do this.

I assume he is getting new speakers so then you just wire the speakers to the amp like normal. Also, for the remote turn on for the amp, you need to wire it to the 12v ignition wire that goes to the back of the stock stereo.

 

Thanks for your help, but k just finished it... here's how I did it.

Looked up wiring amp to factory head unit in 01 toyota celica, looked at the web page, then wired accordingly. I didn't install new speakers, just a sub. I ran all of the wires to the back of the head unit.

I noticed its awful quiet on here for a rainy day...