Wire gauge matches current load for efficiency and safety

Steps:

• Identify circuit functions: Ignition switch controls low-power signals; starter motor draws high current to crank the engine.
• Recall wire properties: Resistance R = ρL/A, where thicker wires (larger A) reduce resistance for high-current paths.
• Compare needs: Starter requires low-resistance path to minimize voltage drop and heat; ignition needs minimal wire to avoid signal loss.
• Conclude: Wire thickness scales with current to prevent overheating and ensure performance.

Why D is correct:

• Starter motors draw hundreds of amps (high current) per Ohm's law (I = V/R), while ignition circuits carry milliamps, so thin wires suffice for low current without excessive resistance.

Why the others are wrong:

• A: Circuits carry different currents based on load, not the same.
• B: Thicker wires heat less due to lower resistance, not more.
• C: Thin wires have higher resistance, increasing voltage drop.

Final answer: D