RS3 Light System Goes Haywire, Random Switch Issues

My 2018 RS4 had a very similar electrical problem with the lighting system last year. Having some experience working on cars, I initially thought it was the headlight switch itself, but it turned out to be more complex. The symptoms matched exactly, unusual activation of dashboard lights and headlights, plus error codes. After taking it to the workshop, they diagnosed a faulty cable connection near the main lighting control module. The wire insulation had worn through, causing intermittent shorts in the electrical system. The repair involved replacing the damaged wiring harness section and properly securing the new connections. Total cost was 95 Euro, including diagnostics and labor. The actual repair took about 2 hours. To better assist with your specific case, could you share: Which error code is stored in your system? Does the issue occur more frequently when driving over bumps? Are there any other electrical components acting up? Have you noticed any correlation with weather conditions? These details would help determine if your car has the same root cause as mine or if its potentially a different automotive switch issue.

After my last service at 164740 KM, I ran a full diagnostic scan and can confirm error code P0650 keeps appearing. The dimmer switch and headlight switch both act up mostly during wet weather. The symptoms get worse when driving on uneven roads, suggesting its likely a wiring connection issue rather than a faulty car switch. The dealer quoted 380 Euro for diagnostic and repair, which seems high compared to your experience. Could you share which repair shop handled your fix? Also worth noting the dashboard lights started flickering right after a recent heavy rainfall, which might point to water ingress somewhere in the system.

Thanks for those additional details. Since I dealt with a similar issue, I can definitely shed more light on your situation. The P0650 code combined with the weather sensitivity strongly points to water infiltration affecting the wiring harness, exactly like my case. The symptoms getting worse on bumpy roads matches perfectly with what I experienced before finding the proper fix. The 380 Euro quote seems excessive given the likely scope of work. The headlight switch itself isnt the culprit here, its almost certainly a wiring issue near the fuse box or main lighting control module. My repair was much cheaper because the shop focused directly on the wiring rather than replacing entire components. A few key points from my experience: Water typically enters through a damaged grommet near the main lighting harness, The car lighting system becomes more erratic during wet conditions due to corrosion, Dashboard lights flickering is a classic symptom of poor ground connection I would recommend checking independent shops that specialize in automotive electrical repairs rather than the dealer. They often have more focused experience with these specific wiring issues and typically charge less for the same fix. Given the identical symptoms, you might want to specifically request inspection of the wiring harness near the lighting control module. This targeted approach should save both time and money.

Thanks for the detailed response and wiring harness information. The connection between water exposure and the electrical problem makes total sense, especially since the dashboard lights and other issues started right after that rainfall. Your repair experience matches my symptoms so closely that Im confident its a similar wiring fault rather than a faulty car switch problem. The P0650 error code appearing after bumpy roads really confirms the loose connection theory. Ill skip the dealer quote and look for a specialist electrical repair shop instead. 380 Euro does seem way too high when the fix might just need wiring harness repair near the fuse box rather than replacing entire components. Will get it checked out this week focusing on the lighting control module area you mentioned. The weather sensitivity and location of the problem should help the mechanic pinpoint the issue faster. Thanks for saving me from potentially wasting money on unnecessary parts replacement.