Electrical, Starting, and Charging Systems
Electrical parts questions test knowledge of battery, starting, charging, and lighting systems and the application-specific nature of each component.
Concepts you must know
- Batteries: group size, cold cranking amps (CCA), reserve capacity, and terminal orientation. Medium-heavy trucks often use multiple batteries in parallel; all should match in age and specification.
- Starters: match by engine, voltage, and mounting; gear-reduction and direct-drive types differ.
- Alternators: match by amperage, mounting, and regulator type; some require specific pulley ratios.
- Lighting: LED vs. incandescent; sealed vs. serviceable; voltage and connector type.
- Wiring and protection: fuses, relays, and harnesses; connector keying prevents mis-installation.
Traps in questions
- Mixing battery group sizes or CCA ratings in a parallel bank.
- Assuming any alternator of the same amperage fits - mounting and pulley differ.
- Forgetting that LED lighting may require compatible flashers or load resistors.
- Overlooking voltage (12V vs. 24V) in multi-battery systems.
Rule of thumb
Match electrical parts by voltage, amperage, and mounting. When replacing batteries in a bank, replace as a matched set to avoid imbalance - a single weak battery drags the whole bank down.