Also on the wiring, take a coil, why do they use a smaller gauge wire for the return? Does it not receive the same power as its larger brother? If its for easy recognition, wouldn't the wire colour coded suffice?
You can almost see your mind ticking over 
. This is a question that a good electrical apprentice will ask in about their second year. It is not so much the power but the current each coil draws or allows to pass though it when activated. Larger wires handle more current. The return can be smaller because it only needs to handle the current returning from that particular coil. The supply on the other hand feeds several coils so potentially needs to handle the current for several coils added together and a good designer would size the wire to handle the current if say all the coils were on. You could indeed reduce the supply wire size as you go down the loom as the potential current draw is reduced but for ease of install it is kept the same.
so putting a heavier wire would not have been a problem. I find the lighter gauge wire on a coil seems to be the one most often that will break off. Dunno if a larger gauge would alleviate this problem.
