i'm no electronic genius, but here's my two cents.
(fyi, i am using a docking station so i do not have to solder to the laptop)
if you still want to run a switch to your laptop
1) dont solder to the ribbon cable. solder to the legs of the power button.
2) to find out which connection makes the laptop turn on is very simple. you could get a continuity checker (excuse my technical name) to determine what contacts are connected when the button is not pressed, vs pressed. if you want to do it half-assed, just put a piece of metal, like a screwdriver across the leads in different combinations until it boots up.