The brief
The Golf had faulty tail lights, sections of the rear cluster not lighting up. He brought it in. A car with dead tail lights is a real risk of getting rear-ended at night or in the rain, and it's a safety and a legal issue, so it's not something to leave. On this Golf the rear lights are LED clusters, where the bulbs and the circuit board are sealed into the assembly. When the LEDs or the board fail, you can't just swap a bulb, the whole tail light assembly has to be replaced. So with sections of the cluster dead and not down to a fuse or wiring, the affected assemblies needed renewing.
The diagnosis
A check confirmed it, sections of the tail light clusters were dead, the LEDs and the boards inside the assemblies failed, with the wiring, the connectors and the fuses all fine, just the assemblies themselves at the end of their life. Nothing deeper. That's a tail light assembly replacement, complete units rather than bulbs, fitted and the lighting checked all round.
The work
The boot trim was accessed, the failed tail light assemblies removed, and new genuine VW-spec tail light units fitted, connected up, every fixing torqued and the trim refitted. The full lighting set, tail lights, brake lights, indicators, reversing lights, was run through to confirm everything worked. A check confirmed all the rear lights lit and bright, the indicators flashing at the right rate, and no warnings on the dash.
The outcome
All the rear lights working and bright, the brake lights and indicators all lit, the rest of the lighting checked, and no warning on the dash. The Golf went home with the tail lights sorted. Faulty LED tail lights only get worse and a dead rear light is a real safety risk, so replacing the affected assemblies put the lighting back where it should be.