Electrical Systems 9/10/25

What is Electricity?

• Electricity is studied differently by disciplines:
  • Scientists: study atoms, electrons, valence rings, repelling charges, and unseen phenomena.
  • Engineers: electricity as a form of energy, circuit designs, and math formulas.
  • Automotive technicians: electricity as a source of customer complaints and a difficult problem to diagnose and repair.
• This program provides essential electrical knowledge for automotive service technicians to find and fix electrical problems.
• A glossary of key terms is provided at the end of the manual.

The Big Three: Volts, Amps, Ohms

• Volts (electrical pressure)
  • Electricity will not flow unless something forces it. A battery or generator creates electrical pressure called voltage; this is the power source.
  • Analogy: voltage is like pressure pushing water through a hose.
  • When you hear volts, think electrical pressure.
• Amps (electrical current)
  • Current is the flow of electricity, analogous to water flow.
  • Measured in amperes (A); moving water is gallons per minute, moving electricity is amps.
  • When you hear amps, think electrical flow.
• Ohms (electrical resistance)
  • Resistance slows current, like a kink in a pipe reducing water flow.
  • Measured in ohms, symbol: oldsymbol{ oldsymbol{ ext{Ω}} } (Omega).
  • When you hear ohms, think electrical resistance to flow.
• Ohm’s Law relation (conceptual):
  • Voltage drives current through resistance: $V = I imes R.$ (Where $V$ is voltage, $I$ is current, $R$ is resistance.)

Conductors, Insulators, and Ground

• Conductors vs. insulators
  • Conductors: metals that allow easy electrical flow (low resistance).
  • Insulators: rubber, plastic, glass (high resistance).
• Ground and common ground
  • In vehicles, wires connect components into complete paths called circuits.
  • Ground paths often use the chassis/body as part of the circuit (common ground).
  • Ground symbols indicate a reference point with minimal potential (often 0 V).
  • Automotive ground paths are typically not insulated on the metal chassis; the path is through metal parts.

Circuit Types and Components

• Five major types of electrical components in circuits:
  • Power Supplies (e.g., batteries, alternators)
  • Conductor Paths (wires, terminals)
  • Electrical Loads (devices that use electricity: motors, lights, coils, speakers)
  • Control Components (switches, relays)
  • Protection Devices (fuses, fusible links, circuit breakers)
• Series vs. Parallel circuits
  • Series circuit: a single path for current; if any element breaks, current stops everywhere.
  • Parallel circuit: multiple branches; each branch receives current independently; loads can be on different branches.
  • Series-Parallel (combination) circuits exist and are common in automotive circuits.
• Common terminology
  • Electrical loads: components that do work (light, heat, motion, sound) and have resistance.
  • Control components: switches, relays that control loads.
  • Protection devices: devices that protect circuits from overload.

Using the Voltmeter Function (DMM)

• How to use the voltmeter
  • Set rotary dial to "V".
  • Test leads: red lead to the positive side of the circuit, black lead to the negative side.
  • Voltmeter is connected in parallel across the portion of the circuit being measured; if placed in series, readings will be incorrect (though meter itself is generally not damaged).
• Key concept: the voltmeter measures electrical pressure difference across two points (potential difference).
• Activity reference (Figure 1-7): voltmeter leads at E (red) and F (black) across a bulb.
• Typical measurements and expectations (example data from activities):
  • Voltage across first bulb (E–F) readings around:
  • e.g., $6.428 ext{ V}$ and $6.188 ext{ V}$ in different configurations.
  • Between points G and H: around $6.263 ext{ V}$ (example from the activity data).
• Common procedure notes
  • If a voltmeter is placed correctly, it will show the potential difference; readings reflect the relative voltages of points in the circuit.
  • Reversing leads will show a negative sign for the reading.
  • A good grounding practice: measure with the black probe on a good ground and the red probe on the test point to determine available voltage at that node.

Activity 1: Basic Circuits and Measurements

• Wiring setup (Figure 1-1):
  • Use red jumper wires to connect the power side (+): A–H, B–C, D–E, F–G.
  • This represents the supplied power; with all components connected and the switch closed, there is a complete path for electrical flow.
• Questions and key points: 1) Is there electricity flowing (light on) when the circuit is complete? Yes, if there is a power source and a complete path. 2) Two electrical power sources used in automotive vehicles: Battery; Alternator. Note: Color coding recommendations for building basic circuits:
  • Red jumpers for power side (+).
  • Black jumpers for ground side (-).
  • Other color jumpers can be used for branch circuits to aid understanding.
• Figure 1-2 (Power supply wiring):
  • Remove the wire between A–H; add red wire from power supply + to A; add black wire from power supply − to H.
  • Wires A and H remain in place for subsequent activities.
• Questions: 3) With the switch closed, do lights come on? (Answer depends on wiring and power supply.) 4) With the switch open (toggle left), is there electricity flowing? No. 5) If you disconnect any wire with the switch closed, what happens? A complete path is required for electricity to do work; without a complete path, electricity cannot flow. 6) To have electricity, there must be a ____ and a ____.
  • Correct filling: power source and complete path (closed circuit).
• Additional concepts in Activity 1
  • Power sources, complete path, and open circuits affect whether electricity flows.
  • Open vs. closed circuit concept and the role of switches.
  • Basic terminology: energy that can do work (electricity) requires conditions similar to gasoline in an engine (fuel-air mixture, compression, ignition) to perform work.
• Circuit path and single-path (Series) concept
  • A single path for electrical components is a series circuit.
  • This activity introduces the idea that future activities will cover more about series circuits and other configurations.
• Important technician note
  • Service technicians must be able to use meters and other test equipment correctly to diagnose electrical problems.

Activity 1: Ground Rules and Measurements (Additional Data)

• Important readings and observations (example values from the activity):
  • Final recorded readings on the voltmeter for questions 16–17 (voltage across E–F and G–H):
  • E–F across first bulb: around $6.428 ext{ V}$ and $6.188 ext{ V}$ (depending on configuration).
  • G–H across second measurement: around $6.263 ext{ V}$.
  • Measurements near the end of Activity 1: (example sequence)
  • Point values: 12.67 V, 12.49 V, 6.227 V, 6.226 V, 0 V, 6.226 V, 6.263 V
• Summary takeaways for Voltmeter use
  • Correct polarity matters (red to positive, black to negative).
  • In a properly functioning circuit, voltages vary by component and branch; the sum of voltages around a closed loop should equal the supply voltage (Kirchhoff’s Voltage Law concept).

Activity 2: The Ammeter Function (DMM)

• Purpose: measure current (amperage) in a circuit.
• Setup notes (Figure 2-1):
  • Build a circuit with parallel paths and loads; use red wire along the main path and green wire for a secondary path.
  • Loads visible in the circuit: horn, light bulb, momentary push switch, toggle switch; protection devices include a circuit breaker and fuses (and fusible links).
• Key questions and answers
  1) Which components are electrical loads? (Examples include: horn, light bulb, motor, speaker, resistor, etc.)
  2) Which components are the control components? (Examples include: momentary push switch, toggle switch.)
  3) Can control components be on either the positive or negative side of a load? (Yes, depending on circuit design.)
  4) What component protects this circuit? (Circuit Breaker or Fuses, Fusible links.)
  5) Name two other protective components: a. Circuit Breaker; b. Fuses; c. Fusible links.
  6) Are loads in different paths? (Yes, in a parallel arrangement.)
• Ammeter fundamentals (in-line/series)
  • The ammeter must be connected in series with the circuit so the current flows through the ammeter and its fuse to indicate how much electricity is flowing.
• Activity results (example data for circuit measurements):
  • Current values observed in various branches: 0.072 A (72 mA), 0.050 A (50 mA), 0.022 A (22 mA).
  • The diagram indicates branch currents and the overall drain from the power supply when multiple paths are closed.
• Practical notes for ammeters
  • The ammeter provides a view of current at various locations; correctly wiring in-series is critical to obtain meaningful measurements.
  • The ammeter can help determine if a circuit’s amperage is too high or too low.
  • Commonly used phrase: current (or amperage) is the flow of electricity, sometimes called drain or load current in charts.

Activity 3: The Ohmmeter Function (DMM)

• Purpose: measure resistance (Ω) with the circuit unpowered.
• Important cautions
  • The circuit you test must be without power to avoid meter damage.
  • The ohmmeter provides its own internal battery for testing resistance; disconnect power before testing.
  • Loose or dirty connections can cause inaccurate readings.
• Setup notes (Figure 3-1/3-2):
  • Connect the ohmmeter across the component or portion of the circuit to measure resistance (not in a live circuit).
  • Disconnect the jumper A (power source) before measuring resistance.
• Typical readings (example data):
  • Resistance of first bulb (across #13) ≈ $33.8 ext{ Ω}$ (shown as 33.8 ohms).
  • Resistance of second bulb (G–H) ≈ $34.3 ext{ Ω}$.
  • Resistance to good ground (L–M) ≈ $0.2 ext{ Ω}$.
  • Across an open switch (C–D when open) ≈ $OL$ (infinite resistance).
• Summary definitions
  • Continuity: reading of 0 Ω indicates a good, continuous path (low resistance).
  • OL (∞): indicates an open path, no continuity.
  • Ohmmeter operation requires a complete, unpowered circuit and proper meter connections.

Need-to-Know Review (Electrical Theory and Meter Usage)

• Fill-in concepts (appropriate wording for each):
  1) Electrical pressure is: voltage (pressure of electrons).
  2) Electrical flow is: current (amperage).
  3) Electrical resistance is: ohms.
  4) The five types of electrical components: Power Supplies; Conductor Paths; Electrical Loads; Control Components; Protection Devices.
  5) The three types of electrical circuits: Series; Parallel; Series-Parallel.
• Voltmeter usage (DC) and live circuits
  • The voltmeter is connected in parallel with the portion of the circuit being measured; it compares the pressure across the meter leads and can be used when the circuit is live (powered).
  • The common phrase in the answer key: "in line with, pressure, live" (test-book conventions may vary; the intended meaning is parallel connection for voltage measurement on a live circuit).
• Ammeter usage
  • The ammeter must be connected in series with the circuit to measure all of the electrical flow; it can also be used in a circuit (in a specific configuration).
• Ohmmeter usage
  • The ohmmeter is never used in a live circuit; it must be connected across a component to measure resistance and the circuit must be powered down.
  • The correct conceptual description: tests resistance across a component when the circuit is dead and the ohmmeter provides its own internal power for the test.
• Practical circuit charting and fault scenarios
  • Open fault (Figure 7-2): disconnecting the wire after R1 (D) creates an open in the path, affecting voltage and current distribution.
  • In an open circuit, the ammeter shows there is current flow (0 current) or an open, but it does not help locate the fault location; a voltmeter is often more useful for locating open circuits.
  • High-resistance faults can be created by loose or dirty connections or low-quality components; an added resistance (HR) can be introduced by removing a wire (e.g., between H and I) to simulate a poor connection.
• Circuit chart observations (Figure 7-1 and 7-2 data)
  • Good circuit (series/parallel values in a known configuration):
  • Total voltage: e.g., $12.66 ext{ V}$ across total resistance. Total resistance: about $705.1 ext{ Ω}$ (or $720 ext{ Ω}$ as stated in some sections).
  • Current: $I <br /> ightarrow 0.018 ext{ A}$ (18 mA) in some configurations.
  • Individual branch resistances in a series path: R1 = $352.9 ext{ Ω}$; R2 = $235.1 ext{ Ω}$; R3 = $117.2 ext{ Ω}$; total $R_ ext{total} = 705.1 ext{ Ω}$.
  • Individual branch voltages in a series path: VR1 ≈ $6.325 ext{ V}$; VR2 ≈ $4.213 ext{ V}$; V_R3 ≈ $2.100 ext{ V}$.
  • Open fault scenario (Figure 7-2): measure across open D–E; observe the following conceptual outcomes:
  • Total circuit voltage vs. individual branch voltages change when an element is opened.
  • In an open circuit, the ammeter reads zero current through the open path, but the voltmeter may show voltage across other parts of the circuit depending on the layout.
  • The open location is often diagnosed by comparing expected voltage drops and resistances against measured values.
• Troubleshooting guidance
  • Should voltage drop occur across an ideal load? Yes, voltage drops exist across loads with current flow according to Ohm’s law.
  • Should there be a voltage drop across a closed switch, wires, connectors, or grounds? Yes, generally there can be small drops depending on contact resistance; however, in some cases, very low resistance paths should show negligible voltage drop.
  • When diagnosing problems, use meters to quantify voltage, current, and resistance at different locations to locate faults rather than guessing.
  • To fix an open fault, restore the connection (reconnect the wire at the open location).
  • High resistance faults (HR) can be created by loose connections or degraded components; removing a component to simulate HR helps study how readings change.

Final practical notes for students

• Always verify meter connections before taking measurements.
• Ensure the circuit under test is powered off when using the ohmmeter.
• When measuring with the voltmeter, ensure the meter is connected in parallel and that the circuit is live if you intend to measure operating voltage.
• When measuring with the ammeter, ensure it is placed in series with the load so all current passes through the meter.
• The DMM provides multiple measurement modes; use the correct port and range for each measurement (volts, amps, ohms).
• Real-world relevance: understanding voltage, current, and resistance helps diagnose automotive electrical faults, select appropriate fuses, and interpret readings when repairing circuits.