Voltage drop across fuses and finding active circuits
Why do you sometimes measure almost 0 V across a good fuse, but battery voltage across a blown one?
What this lesson covers
CORE TEACHING Voltage across a component; good fuse near-zero drop; blown fuse becoming open circuit; mV fuse-drop technique as a clue to current flow. PRACTICAL DEMONSTRATIONS AND TESTS Measure across good powered fuse; blown fuse; compare mV across several active/sleeping circuits. ADVANCED / SCAN TOOL LAYER Use fuse mV charts only as supporting evidence; combine with current clamp for parasitic-drain work. KEY DIAGNOSTIC QUESTIONS Am I measuring fuse-to-ground or across the fuse? Is the circuit loaded? What does the voltage difference mean? MUST-COVER CHECKPOINTS Circuit must be loaded; positive side; ground side; connection-by-connection split; compare post-to-terminal; retest after repair.
What you will be able to do
Why do you sometimes measure almost 0 V across a good fuse, but battery voltage across a blown one?
Where it sits in the programme
- Builds on
- Lesson 12: Automotive fuses
- Feeds into
- Lesson 14: Relay testing