2004 and earlier radio harness adapters for 2005 upgrade JBL radio and external amp?

[two37]

Hello, I have a 2004 Corolla LE and would like to install a 2005 upgrade JBL 6-CD radio (86120-02450) and matching JBL external amp (86120-02010) but the connectors on my wiring harness are not compatible (pre 4/2004?). I bought the radio/amp combo very inexpensively off of ebay because the radio that was in my car when I bought it (an aftermarket JVC piece-of-cr_p) died. Here are my questions:

1. Are ALL 3 radio ports and BOTH external amp ports utilized once installed? This is an important question to be answered because my external amp came with a pigtail on 1 of its 2 ports (the larger of the 2) AND I have found a reseller who is selling the same radio WITH a pigtail on 1 of its 3 ports (the largest of the 3); he won't sell me the pigtail separately but I may still buy them from him anyway then simply relist the radio on ebay just to get the radio pigtail IF it is, in fact, the only port being used once it’s installed. I have tried to locate the pigtails separately for both the radio and external amp for the purpose of making my own harness adapter but have had no success; I am an Electrical Engineer by trade so I consider myself to be very handy at things like this.

2. Instead of "re-inventing the wheel", does such a harness adapter already exist?

3. Where can I find a pin/wiring diagram/table for BOTH the radio AND the external amp?

Any suggestions or info is greatly appreciated. Please feel free to contact me directly at two37@yahoo.com. Thanks, Chris