Electrical and Electronics
Electrical inspection on heavy trucks centers on batteries, starting/charging, lighting, and the wiring that ties them together. Understand battery basics: state of charge, specific gravity or open-circuit voltage, load testing, and the importance of matched batteries in parallel. Know that a weak battery in a parallel set drags the others down and that corroded or loose terminals cause voltage drop and hard starting. Charging system checks include alternator output voltage and amperage, belt condition, and inspecting cables for chafing and correct routing.
Lighting and wiring inspection: verify all lamps operate (head, marker, clearance, turn, brake, backup), check for correct operation of turn signals and four-way flashers, and inspect connectors for corrosion and water intrusion. Understand voltage-drop testing as the preferred method to find high-resistance connections rather than guessing at components. Recognize that a blown fuse points to a circuit fault-replacing the fuse without finding the cause is a trap.
Common traps: reading surface charge as true battery voltage (apply a load or let it rest), assuming a charging problem is the alternator when it is a belt or cable, and overlooking grounds. Another trap is mistaking a bulb that works intermittently for a bad bulb when the socket is corroded.
Rule of thumb: chase voltage drop, not parts. Worked example: a slow crank. Measure battery open-circuit voltage after rest; if low, charge and load test. Then check voltage drop across cables and grounds while cranking-more than about 0.5 V on a cable suggests a bad connection to clean or replace.