The right-hand headlight stays dark while the left one works.
A single lamp is inoperative. The fault is isolated to that lamp circuit rather than the whole lighting system.
Suggested test plan
- Confirm the symptom and check the fuse.
- Measure voltage at the lamp connector.
- Measure the bulb filament and ground.
- Repair the open circuit and re-test.
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.
Single-lamp faults are usually the lamp, its connector or its local ground. A shared fuse would affect both lamps.