Celica Forums General Discussion Exterior stereo wiring question

I am about to install my head unit (hope I don't get that alternator noise I been reading about). I am going to bypass the factory amp. I went through the installs section and came across the wiring for a gts . I got a few questions.

Caps are main color followed by stripe.
HEAD UNIT
GRAY w/silver dots 12V ACC
BLUE w/yellow stripe 12V Constant
WHITE w/green dimmer
WHITE sig left front <------what is this
YELLOW sig left rear <------ this
RED sig right front <------this
BLUE sig right rear <-------- this
GRAY/shrink sig shield (all) <----- and this ?????

what is sig. I am guessing its signal but i am not sure.

yes sig means signal

where do i connect the sig wire to than. Are does the wires the power the speakers??? If not, that what are they 4 ????

found a good link for this problem.
2000 gts amp bypassing instructions [celica.net]