100w = 8 ampswhats a standard H4 bulb normally use??
P.s. Not being a smartarse but i think your componant power consumption is off by a lot... Thermo's (even the smaller ones) pull an average of 15 amps each when running and peak current can reach 30ish on start up!
The fuel pumps should run at 6-7 amp when running at idle, more than this would often indicate a restriction problem and less would often be caused by a poor pump or reg.
Can you get hold of a clamp meter and see whats being made?
P.p.s. Over kill is waayyy better than under kill when it comes to sizing automotive cable