Log #14 - Rear Lamp Bulb Carrier Corrosion and Wiring Repair

Fault Symptoms and Bulb Checks

The right rear parking light became intermittent, followed by failures of the right turn signal and reverse light. Each bulb filament was checked with the continuity buzzer on a UNI-T UT33C+ multimeter. The bulbs tested good, pointing the investigation toward the corroded bulb carrier and its electrical contacts.

Cleaning the Bulb Carrier

Rust and oxidation were visible on the carrier. The board was removed and the affected areas were cleaned with 400-grit abrasive. An intermediate continuity check showed that electrical conduction had returned. All corroded conductive paths were cleaned carefully.

Correcting the Reverse-Light Bulb Position

During reassembly, the reverse bulb had mistakenly been placed in the fog-lamp socket. The factory fog-lamp circuit was present but inactive in the right rear lamp cluster on this Golf Mk4. Moving the bulb to its correct socket restored the functions and avoided an unnecessary parts purchase.

Protecting the Repaired Contacts

Because sanding removed part of the original protective coating, dielectric grease was applied after the carrier was removed and the contact areas had been cleaned. The wiring insulation was also found to be worn; replacing the harness tape and protective sleeve was recorded as a future task.

Conclusion and Follow-up

All rear-lamp functions were stable after the repair. Further work planned includes renewing the worn wiring protection and researching an OEM-aligned way to activate the right rear fog lamp, rather than making an unverified wiring change.