Wiring and joining up all those electronic boxes is becoming increasingly important on the modern race car.
Size of conductors - not to be confused with the size of the insulation. Cheap insulators like PVC need to be thicker than Tefzel to do the same job, so dont confuse a big cheap wire with a quality skinny one. It is likely they can both carry the same current.
Insultation - have a look through the table. General automotive cable is PVC and melts when it gets a little overheated. Mil spec cables are coated with PTFE or ETFE, ( often referred to as Tefzel ) and in some cases like Type 44 it has 2 layers. Mil specifications generally run from -65 to 150 degress before the insulation breaks down.
Tin plating. Copper by itself corrodes to a nice green colour. Exposed ends need to be tin plated to ward this corrosion off.
Current capacity. All copper carries the same amount of current. Note the tables below for type 44 and 55 cable. For a given size the current a wire can carry is the same. Work out how many watts a circuit will carry and divide by 13.4 ( most alternators output 13.4 volts ) to arrive at what a given circuit would be expected to carry. Apart from starters most automotive circuits do not carry many amps.
Specifications sold on this web site :
M22759/32. This has become the motorsport standard outside Europe. Tin plated and coated in ETFE, more commonly know as Tefzel. Temperature range from -65 - 300. The insulation is highly resistant to high PH cleaning fluids, fuel, lubricating oils, and many other chemicals.
Raychem Spec 44. This is tin plated and rated to 150 degrees. The dual wall dual wall construction of Spec44 wire is highly resistant to many acids, alkalis,hydrocarbon solvents,fuels, lubricants, water and many missile fuels and oxidisers.
Dual wall - this is where the inner wall is white and covered with another colour on top. The military particularly like this as any nicks or abrasions show up in the inner white colour. This makes spec44 very slightly larger in diameter than spec55.
Raychem Spec 55. Similar to spec44 but with a single wall insulation of cross-linked ETFE polymer