Occupational safety, hand tools, test equipment and workshop practice
Occupational Safety in the Auto Electrical Workshop
The vehicle is a hazardous-energy box
A 12 V lead-acid battery can deliver 600–1000 A into a spanner dropped across its posts, melting metal and spitting acid. Safety questions are usually about hazard classification and control, so learn the groups: chemical (sulphuric acid, refrigerant, solvents - read the SDS and know the first-aid measures), electrical (short-circuit burns, arcs, stored energy in capacitors, high-voltage traction systems), gas (hydrogen from gassing batteries, exhaust fumes), mechanical (belts, fans, hot exhausts, lift points) and pyrotechnic (SRS airbag modules).
Match PPE to the task: safety glasses or a face shield for battery and refrigerant work, acid-resistant gloves and apron, nitrile gloves for fluids, steel-toe boots, hearing protection. Ventilate when charging, and ban smoking, grinding sparks and naked flames near a venting battery.
Traps that appear in questions
Choosing water on an electrical fire (isolate, then CO2 or dry powder); skipping PPE for a 'quick test'; lifting a battery by its terminal posts; reversed-polarity jump starting; assuming 12 V cannot hurt you (burns and eye injury are the real risk); removing an airbag module without disabling the SRS and waiting the specified capacitor-discharge time; and touching a hybrid/EV traction circuit without HV qualification, approved gloves and lockout/tagout.
Rule of thumb. Disconnect the negative terminal first and reconnect it last, so a spanner cannot bridge the positive post to the chassis. Terminal-to-chassis short: I = V ÷ R = 12 V ÷ 0.01 Ω = 1200 A - that is why the earth lead comes off first.
Hand Tools, Test Equipment and Workshop Practice
Choosing the right instrument
Candidates must know what each instrument actually measures and its loading effect. A digital multimeter (DMM) reads volts, ohms, amps and continuity, but current must be measured in series or with a clamp meter; never put the meter across the supply in amps mode. A low-impedance test light draws enough current to damage ECU drivers and data lines - use a high-impedance probe, logic probe or scope on those circuits. A power probe or bi-directional test tool can supply power and ground safely, and an insulation tester checks for leakage at high voltage with the circuit isolated.
Hand tools: use the correct size socket or spanner to avoid rounding fasteners; a click-type torque wrench must be stored at its minimum setting and never used to undo fasteners; micrometers, vernier calipers and feeler gauges must be zeroed and clean. Good workshop practice covers clean and organised benches, correct jacking and lifting points, wheel chocks, no loose tools under the bonnet, correct fastener torque and thread repair rather than over-tightening.
Traps
Measuring resistance with the circuit powered; trusting a meter that has not been zeroed; using a test light on a sensor reference or CAN line; leaving a torque wrench wound up to maximum; probing the back of a sealed connector and spreading the terminal; and condemning a component from a resistance reading without checking voltage drop under load.
Worked example. An injector reads 0.5 Ω but your leads add 0.3 Ω, so the meter shows 0.8 Ω. Touch the probes together first and subtract - for any reading under 10 Ω, always compensate the leads.