I have one tail light out of 4 on the tail gate that does not work. I have changed 2 bulbs and still nothing.
Check for electrical grease corrosion. It is very common and can limit the connection. Inspect your Wiring as Well.
happens to me non stop .. i change my rear tail lights probably every 2-3 months.
by the way .. no corrosion and have had the wiring checked numerous times.
It is possible it could be a short, open circuit, or frayed wire. In that area the wiring is very small and easily damageable.
Also had continual brake/tail light failures. Got advised to change all 4 bulbs together and to only use Audi/bosch bulbs . Did this and no problems since
Search Audi Q7 Questions
Audi Q7 Experts