This electrickery is all a big con its all about smoke.
When smoke pipes (wires) fail they emit smoke.
Generators/alternators are just smoke prducing machines.
Rectifiers just direct the smoke in the right direction.
Batteries are just smoke storage cells.
Starter motors are smoke powered motors and need a lot of smoke to turn the engine over hence the larger pipes.
Bulbs are small pipes that produce light by forcing smoke through the small pipes with friction causing heat/light.
Electronic components get burnt when to much smoke is put through them.
Coils convert low pressure smoke into high pressure smoke.
HT leads are high pressure smoke carrying pipes.
Spark plugs are full of sparks obviously which gets knocked out of them by high pressure smoke and need changing when all the sparks are knocked out of them.