Body Electricals and Vehicle Accessories
Body Electricals and Vehicle Accessories
This domain tests 12 V electrical diagnosis, wiring repair, accessory installation and safety-system precautions. The exam expects measurement-based diagnosis rather than parts swapping.
Core rules
- Use a digital multimeter for voltage, resistance and voltage drop. A voltage drop test under load finds high-resistance connections that an ohmmeter may miss.
- Check battery state of charge, fuses, relays and grounds before replacing components. A relay can be tested by coil resistance and load operation.
- Disconnect the battery before working on airbags, and never probe airbag connectors with a meter. Wait the specified time for capacitor discharge.
- Repair wiring with crimped and sealed connections or soldering with heat-shrink; do not pierce insulation for tests unless the hole is sealed.
- CAN bus faults can shut down multiple systems; check power, ground and bus resistance before condemning modules.
- Accessories must be fused and routed away from moving parts and heat.
Worked example
A power window works slowly. Reasoning: measure battery voltage, then perform a voltage drop test on the power and ground circuits while the motor runs. A high drop indicates resistance at a connector or ground. Cleaning the ground may restore speed; replacing the motor first would waste time.
Traps
Probing airbag circuits; using a test light on delicate electronics; piercing insulation; wrong crimp; adding an unfused accessory.
Key points
Voltage drop testing finds resistance under load. Check battery, fuses, relays and grounds first. Never probe airbag circuits with a meter. Use sealed crimps or soldered, heat-shrunk repairs. Accessories need fusing and safe routing.