The Brake Light runs off Fuse 4. That is the Blue/Yellow Wire in the Loom. This also runs the Horn, the Blinkers (Turn Signals) and the Speedo.
Does the little Blue High Beam indicator light come on when the High Beam is on?
Have you checked the Globe in the Headlight?
The Headlight, rear Tail light and Number Plate Light (License Plate Light) run off Fuse 3. This is the Yellow Wire in the Loom.
The Yellow Wire goes from Fuse 3 to the Light Switch. You should be able to measure 12V on the Yellow Wire at the Light Switch (engine must be running).
The Wires from the Light Switch are Blue for High Beam and Green for Low Beam.
The Green goes straight to the Headlight socket from the Light Switch.
The Blue goes to both the Headlight socket and the little Blue High Beam indicator light.
Check for an Earth on the Brown Wire out of the Headlight socket.
Having an uneducated guess , I would say it is maybe the Light Switch. A bit of WD40 in the Switch might fix it.
