Voltage on a real vehicle
A component has 12 V at its connector but still does absolutely nothing. How can 12 V be there and the circuit still be faulty?
What this lesson covers
CORE TEACHING Potential difference; reference point; open circuit voltage; loaded voltage; supply and return path; why voltage is measured between two points; ghost/back-fed voltage. Add practical series vs parallel circuits; shared feeds and shared grounds; basic Ohm’s Law (V=IR) only as a diagnostic tool; why parallel loads each receive system voltage; how resistance before a branch can affect multiple loads. PRACTICAL DEMONSTRATIONS AND TESTS Measure battery positive to negative; positive to body; component supply to ground; unplug a load and compare; load the circuit with a lamp. Build a simple series lamp circuit, then a parallel two-lamp circuit; introduce resistance into the shared feed and watch both branches change. ADVANCED / SCAN TOOL LAYER Show live data voltage if useful. Introduce PWM/controlled outputs as a reason strange average voltages may appear. KEY DIAGNOSTIC QUESTIONS Where am I placing both probes? Is the circuit loaded? Is this a real supply or a weak/back-fed supply? MUST-COVER CHECKPOINTS Start with the complaint; draw the circuit; identify expected inputs/outputs; perform physical tests; interpret evidence; prove the failed section; retest after repair.
What you will be able to do
A component has 12 V at its connector but still does absolutely nothing. How can 12 V be there and the circuit still be faulty?
Where it sits in the programme
- Builds on
- Lesson 1: Battery testing from start to finish
- Feeds into
- Lesson 3: Grounds and bad earths