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Voltage-drop testing: finding a bad connection under load

A connection can pass an ohms or continuity test and still fail under load. Measuring voltage across a switch, connector or wire while current flows shows where power is being lost. A good closed contact drops almost nothing; a bad one drops a noticeable part of the supply.

Single source ~30 min moderateBrands: All

Before you start

This is a live test: insulated probes, clips placed with power off where possible, keep clear of terminals
Never back-probe in a way that can short adjacent pins

Diagnostic steps

Unlock all 4 steps with expected values

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OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work.

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