Voltage OK but Device Dead? Troubleshooter
A good voltage with nothing running can hide a bad connection.
A meter draws almost no current, so a bad joint can still show full voltage. Work through one question at a time. You can go back or start over whenever you like.
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Safety: this troubleshooter is general information for low-voltage DC learning circuits. 240V AC mains can kill: in Australia, work on mains wiring must be done by a licensed electrician. Disconnect power before you touch wiring.