SVP Auto Electrician cheat sheet

Lockout/tagout isolates hazardous energy; verify zero energy at the point of work before touching conductors or moving parts.

Lead-acid charging releases hydrogen; keep flames, sparks, and smoking away and ventilate the area.

Battery electrolyte is sulfuric acid; flush skin or eye contact with water for at least 15 minutes and seek medical help.

Hybrid/EV orange cable is high voltage; do not cut, probe, or disconnect without manufacturer procedure and rated PPE.

Engine exhaust contains carbon monoxide; never run an engine in an enclosed bay without exhaust extraction.

Use jack stands rated for the load under structural chassis points; a jack alone is not a support.

Electrical fires use CO2 or dry chemical extinguishers; water conducts and can spread energized electrical hazards.

Eye protection is required for grinding, compressed air, battery service, and any operation that can throw particles.

Voltage is measured in parallel; current in series; resistance/continuity only on a de-energized circuit.

A clamp meter measures current from the magnetic field and must clamp only one conductor.

A multimeter CAT III rating is appropriate for vehicle and charging-system circuits; use a fused current input.

Torque wrenches are used within their specified range and checked periodically; torque to manufacturer value and sequence.

Insulation resistance testers apply high voltage; isolate and discharge the circuit before testing.

Feeler gauges measure plug gaps and valve clearances; plastigauge measures bearing clearance.

A test lamp must be rated for the circuit current; use an LED or high-impedance probe on electronic circuits.

Calipers and micrometers are zero-checked before measurement; measurement is taken at a consistent temperature.

Ohm's law: V = I × R; power: P = V × I = I²R = V²/R.

Series: R_total = R1 + R2 + ...; current is common; voltage divides in proportion to resistance.

Parallel: 1/R_total = 1/R1 + 1/R2 + ...; voltage is common; current divides inversely with resistance.

Kirchhoff's current law: sum of currents entering a node equals sum leaving; voltage law: sum of voltages around a loop is zero.

A silicon diode forward drop is about 0.7 V; germanium about 0.3 V; reverse bias blocks current.

An NPN transistor turns on when base-emitter voltage is about 0.7 V; base current controls collector current.

A capacitor stores charge; time constant τ = R × C; it blocks steady DC and passes changing signals.

A magnetic field surrounds a current-carrying conductor; a relay coil uses it to operate contacts.

Voltage drop under load reveals resistance: a connection above about 0.1 V or cable above about 0.3 V warrants investigation.

Rested 12 V lead-acid state of charge: about 12.6 V full, 12.2 V half, 11.8 V or lower discharged.

Remove surface charge with a load before open-circuit voltage testing.

Alternator charging voltage is typically 13.5–14.5 V at normal temperature.

During cranking at 20 °C, battery voltage should generally stay above 9.6 V.

Battery load test: apply about half the CCA rating for 15 s; voltage above 9.6 V at 20 °C is acceptable.

Series battery connections add voltage; parallel connections add capacity while voltage stays the same.

AGM and EFB batteries require compatible charging profiles; a standard charger can overcharge or damage them.

Parasitic draw is measured after modules sleep; many vehicles specify below about 50 mA.

High-current headlamp circuits use a relay; battery feed → fuse → relay → lamp → ground.

Halogen bulb glass must not be touched; finger oils create hot spots and shorten life.

HID lamps use a ballast and high starting voltage; disconnect power and wait before service.

LEDs are polarity-sensitive and may be dimmed by PWM; low current can trigger bulb-out warnings.

A thermal flasher may hyperflash with LED turn signals; use an LED-compatible flasher or load resistor.

A dual-filament brake/tail bulb shares a common terminal; the brake filament is brighter, and a bad ground causes cross-feed.

Headlamp aim must follow the manufacturer or applicable beam pattern; incorrect aim causes glare and poor visibility.

A fuse protects the wire; its rating must not exceed the wire's current capacity.

Never install a larger fuse to stop blowing; find the cause of excess current.

Fusible links protect main feeds; circuit breakers may reset automatically or manually.

Relay terminals: 30 battery feed, 87 load output, 85/86 coil, 87a normally closed contact.

A crimped terminal must pass a pull test; solder is not a substitute for a proper mechanical crimp in vibration.

Sealed connectors use weatherproof seals and dielectric grease; piercing insulation creates corrosion paths.

Wire gauge: larger AWG number means smaller conductor; metric sizes are in mm².

Harness repairs use staggered splices, adhesive-lined heat shrink, and strain relief to preserve flexibility.

Many window motors reverse direction with supply polarity; module-controlled windows may use relays or solid-state drivers.

Express-up/down windows often require initialization after battery disconnect or motor replacement.

The wiper park switch keeps the motor powered until blades reach park, then opens the circuit.

Central locking actuators may be polarity-reversing or one-wire; the BCM controls lock/unlock timing.

Instrument gauges may use stepper motors or network data; fuel and temperature senders typically vary resistance.

The horn circuit uses a relay and a switch that supplies ground or power depending on design.

An immobilizer mismatch can allow cranking but prevent start; key, immobilizer, and ECU must be matched.

ECUs receive sensor inputs and control actuators; check powers, grounds, and 5 V reference before condemning the ECU.

Potentiometer sensors use three wires: reference, signal, and ground; signal voltage changes with position.

NTC thermistors decrease resistance as temperature rises; inductive sensors generate AC voltage.

Hall sensors produce a digital square wave and require supply, ground, and signal.

CAN bus is a twisted pair with two 120 Ω terminators; about 60 Ω is measured across the bus with power off.

CAN-H and CAN-L carry opposite differential signals; a short, open, or missing terminator can disable communication.

LIN bus is single-wire, master-slave, and uses a nominal 12 V dominant level.

PWM actuators vary average current by duty cycle; drivers may be ground-side or power-side.

Verify the complaint, gather symptoms, and perform a visual inspection before connecting a scan tool.

Read current and history DTCs plus freeze frame; a code identifies a circuit or system, not a guaranteed failed part.

Voltage drop testing under load locates resistance better than resistance measurement on an unloaded circuit.

Parasitic draw testing requires modules to sleep; clamp the negative cable and compare to specification.

Wiggle tests flex harnesses and connectors while monitoring data to expose intermittent faults.

Temperature faults can be reproduced with freeze spray or a heat gun while monitoring signals.

After repair, clear codes, operate under the original conditions, and confirm normal data and function.

Use an oscilloscope to inspect injector, ignition, and network waveforms when scan data is inconclusive.