need some help with h/u and wireing harness

[Abterra]

Hey guys, haven't been on here in a while, and decided to create a new account.

I'm having a problem with my system. I have the JBL sound system, and the stock head unit's cassette drive has two broken gears in it, and now makes a horrendous grinding sound every time I try to put a cassette adapter for my Ipod in. * I know this because I disassembled EVERYTHING. . I just went out to best buy (horrible experience) the other day, and picked up a Sony CDX-GT250MP http://esupport.sony.com/US/perl/model-home.pl?mdl=CDXGT250MP&LOC=3&session_id=bcb4b5d96fb3646d8a3663340aa83804 and I cannot install this thing. I am so confused. On the back of my JBL headunit, there is a 12-pin slot (which WAS NOT connected to anything) and a 20-pin wire harness slot (which was connected to my car audio system.) I don't know how to splice the wires to the new harness, and I'm confused on the amp.

I have an external amp somewhere in my car (due to my research) Can I use this Sony h/u if it's amplified? Do I have to bypass the stock amp? please forgive my ignorance in this matter I'm a newb in car audio.

My main questions: 1) can I do this with the stuff I have? 2) do I have to bypass the stock amp? 3) is there an adapter that goes from 20-pin to the wire harness in the sony?

please help,
Thanks in advance, and happy new year!

Tyler

edit: I have a 2003 Solara Coupe w/ JBL sound system

[MisterTedster]

With your head unit, you should most definitely bypass the stock JBL amp. I have not heard good things about using the stock amp and a third-party head unit. There are wire harnesses that you can purchase so that you do not have to splice into your lara's wiring harness like this: http://cgi.ebay.com/2000-Toyota-Solara- ... 3595465fbf

Simply follow the wiring color codes, and you'll be set.

As for powering your speakers, you could certainly power it off your head unit, but you'd get much better sound with an amplifier. With a new amplifier comes new speakers, with new speakers comes installation woes, and that's a whole new can of worms.