Is there a relay for license plate lights and trunk lock?
license plate lights not working and trunk lock wont open with key. Is there a
relay that might be at fault?
Year/Make/Model? I've never seen a relay for the license plate lights in all my years.... but there may be some vehicle out there wired that way. The trunk lock should not be associated with the same circuit, even though they are both in the rear of the car. A coincidentally occurring electrical problem in the same area would have me checking the Molex-type wire junctions ... but having said that, I always start at the inoperative device and keep testing toward the battery-fuse box since you didn't state any other electrical problems are happening. The license plate lights usually are wired in with the side markers ..... either they are bulbs in huge headlamp combo- units or individual side marker housings.
Sorry ... I see this is an Audi. My bad... but the answer stays the same.
Agree with JPV,more than likely bulb or wiring issue,they run off the same fuse and wiring as your tail lights.
Looking for a Used A4 in your area?
CarGurus has 12,042 nationwide A4 listings starting at $950.
Search Audi A4 Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Audi A4 Experts