Automotive Electrical and Electronic Systems
What the exam tests
Automotive electrical and electronic systems covers the battery, starting, charging, ignition, lighting, sensors, ECU, wiring, fuses and multiplexing. Questions test circuit laws, component function and simple fault diagnosis.
Core rules and concepts
- A 12 V lead-acid battery supplies starting current and stabilises voltage. Capacity is rated in Ah; cold cranking current matters in winter.
- The starter converts electrical energy to mechanical torque through a solenoid and motor.
- The alternator charges the battery and powers loads; the regulator holds about 13.8-14.4 V.
- Sensors feed the ECU with voltage signals. Actuators convert ECU outputs into action.
- Series circuits share current; parallel circuits share voltage and allow independent operation.
- Fuses protect wiring; relays allow low-current switches to control high-current loads.
Worked example
A 60 W headlamp operates at 12 V. Current I = P/V = 60/12 = 5 A. Lamp resistance R = V/I = 12/5 = 2.4 Ω. If the wiring and switch add 0.1 Ω, total resistance is 2.5 Ω, current falls to 4.8 A and the lamp receives 11.52 V. The 0.48 V drop explains dim lighting and shows why voltage-drop testing is better than guessing.
Traps that cost marks
- Measuring resistance on a live circuit.
- Assuming battery voltage stays at 12 V while cranking.
- Confusing Ah capacity with cranking current.
- Treating a blown fuse as the root cause without checking the circuit.