A relay buzzes and the load flickers when it should stay on.
The coil is not receiving a stable supply, often because of a poor ground or low control voltage.
Suggested test plan
- Measure coil voltage under load.
- Voltage-drop the coil ground.
- Test a known-good relay.
- Repair the ground or replace the relay.
Safety: 12 V systems are low voltage but can still cause burns and fire. Disconnect the battery before working on wiring and never short a battery terminal.
Relay chatter is usually a voltage supply problem rather than a relay problem. Voltage-drop testing finds it quickly.