Electrical & Electronic Systems (A6)

Ohm's law states current equals voltage divided by resistance (I = E / R); power equals voltage times current (P = E x I).

Series circuits share one path, so an open stops all flow; parallel circuits have multiple paths and a lower total resistance than any single branch.

Two equal resistors in parallel yield half the resistance of one, which increases total current draw.

A fully charged 12-volt battery reads about 12.6 volts at rest; a running charging system should read roughly 13.5 to 14.5 volts.

Slow cranking with a good battery usually means high resistance in the starter circuit, found with a voltage-drop test.

The alternator's diodes rectify AC into DC; a failed diode causes low output and excessive AC ripple.

A voltage-drop test finds unwanted resistance in cables and connections better than a visual inspection.

A fuse that blows again immediately indicates a short to ground or an overload, not a weak component.

Measure voltage with a meter connected in parallel and current with an ammeter connected in series.

Dim lights that brighten with engine speed indicate a weak battery or undercharging condition.

Coolant-temperature and similar gauges rely on thermistor sensors whose resistance changes with temperature.

A relay uses a small control current to switch a larger load, protecting switches and reducing wiring size.

Ground connections provide the return path to the battery negative; a poor ground causes dim or erratic operation.

Parasitic (key-off) draw is measured with an ammeter in series after modules go to sleep, isolating circuits by pulling fuses.

Wiring diagrams show power sources, loads, grounds, and connectors to trace circuits systematically.