Electrical and Electronic Systems
Core concepts
Know Ohm's law (V = I × R), series and parallel circuits, and how to use a digital multimeter. Understand battery construction, starting and charging systems, and the role of the alternator and voltage regulator. Be able to explain relays, fuses, grounds, and how a computer uses sensors and actuators. Know the difference between a short to ground, a short to power, and an open circuit.
Traps to expect
Questions often confuse voltage and current measurements. Voltage is measured in parallel; current is measured in series. A parasitic draw test should use an ammeter in series with the battery, not a voltmeter across it. Another trap is assuming a dead battery means a bad battery: check charging voltage first. Also remember that a poor ground can cause multiple unrelated symptoms, and that a relay coil and contact circuit are separate.
Worked example
A 12-volt circuit has a 3-ohm resistor. Current is V/R = 12/3 = 4 amps. Rule of thumb: if measured current is far lower, suspect added resistance or an open; if far higher, suspect a short.
Study strategy
Practice reading wiring diagrams, measuring voltage drop, and isolating circuits by removing fuses during a draw test.