Automotive Electrical Drawing, Measurement and Trade Science
Automotive Electrical Drawing, Measurement and Trade Science
This domain tests wiring-diagram symbols, DIN terminal designations, units and prefixes, measurement accuracy and basic trade science.
Core rules
- DIN terminal numbers: 30 permanent battery positive, 15 ignition-switched positive, 31 earth or negative, 50 starter control, 61 charging warning lamp, 85 and 86 relay coil, 87 relay load contact, 87a normally closed contact.
- Learn symbols for battery, fuse, relay, motor, solenoid, switch, earth, lamp, diode and sensor.
- SI prefixes: k = 10³, m = 10⁻³, µ = 10⁻⁶, M = 10⁶. Distinguish m (milli) from M (mega).
- Multimeter accuracy is stated as ±(% reading + counts); choose the range for best resolution.
- Resistor colour code: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9; gold ±5%, silver ±10%.
- Trade science includes power, efficiency, magnetism, semiconductors and temperature effects.
Worked example
A resistor is marked brown, black, red, gold. Brown = 1, black = 0, red = ×100, so 10 × 100 = 1,000 Ω = 1 kΩ, tolerance ±5% = ±50 Ω. Acceptable range = 950–1,050 Ω. A meter reading of 960 Ω is within tolerance. If the meter reads 0.96 kΩ on the 2 kΩ range, convert correctly: 0.96 kΩ = 960 Ω. On a wiring diagram, a relay coil between terminals 85 and 86 with 80 Ω draws 12/80 = 0.15 A when energised.
Traps
Confusing terminal 30 permanent live with 15 switched live; misreading m and M; ignoring meter count accuracy; reading resistor colours from the wrong end; treating a wiring diagram as a physical layout; forgetting that relay contact rating must exceed load current.