Automotive Electrical and Electronic Systems
Electrical principles
Ohm's law (V = IR) and power (P = VI) underpin all circuit questions. Series circuits share voltage and have one current path; parallel circuits share voltage and divide current. Battery capacity is in ampere-hours; cold cranking amps indicate starting ability. Know the charging system (alternator with rectifier and regulator) and the starting system (battery, solenoid, starter motor).
Fault finding
Use a logical sequence: verify the complaint, check the fuse and connections, test for voltage drop, then isolate the component. A high-resistance connection causes voltage drop under load. Earth faults cause dim lights and erratic operation. Sensors such as crankshaft position, oxygen, coolant temperature and mass airflow feed the ECU; actuators include injectors and ignition coils. Traps: probing with a test lamp when a high-impedance meter is needed, assuming a blown fuse is the fault rather than a symptom, and disconnecting the battery with the engine running.
Worked example: a 12 V circuit with two 6 ohm resistors in series has total resistance 12 ohm and current 1 A; each resistor drops 6 V. In parallel, total resistance is 3 ohm and current 4 A.
Safety
Batteries release hydrogen; avoid sparks. Use insulated tools and remove the earth terminal first. Electronic modules are sensitive to static and reverse polarity.