looking for a preamp signal in stock head

hi, I'm looking to add a kicker cvr12 and an amp to the Mark Lev. system in my 2003 GS300 since the Mark L system produces good higher tone bass but poor low tone bass. My question is where to get a preamp signal that I can use. Whenever I've installed systems in the past, I worked with an aftermarket head with a simple bass output -_- Thanks in advance!

Amp Turn On     BLACK/ ORANGE     (+)          RADIO HARNESS                LF Speaker (+)          BLACK                LF Speaker (-)          WHITE                RF Speaker (+)          PINK                RF Speaker (-)          ORANGE                LR Speaker (+)          RED                LR Speaker (-)          GREEN                RR Speaker (+)          LIGHT GREEN                RR Speaker (-)          VIOLET use line out converter on rear outs to sub amp. If amplifier in car from factory, then they may be low level.The wire I'm test'n isn't doin' what it's supposed to be doin'... I am so glad I printed that tech sheet, with the wrong info.

Do it right the first time... or I might have to fix it for ya

is there anyway to do it without a line out converter?

my amp has a high level input so would I be able to use the wires that are connected to the stock sub without frying the stock amp?

How many plugs connect to your factory amp?  What type of connectors are they?    When you find the connector with the wires Techman pointed out to you,  Are there other wires on that connector?

there are 3 connectors to the amp. One is a 12 pin, and two smaller ones. I'm starting to wonder if there is a separate amp for the factory sub too.

Did you find the wires Techman identified for you?    If so are there other wires on that same plug?

soldered wires str8 to the factory amp and connected it to high level input on my amp. Worked like a charm.