There are multiple earthing points around the vehicle, with several in the passenger compartment and the engine bay, but if it was an earthing issue we would expect there to be other electrical issues with the instrument panel and other electrical equipment. It could be that the lights themselves are faulty, the wiring is damaged, there is water ingress or a damaged fuse. Tracing an electrical fault such as this can be frustratingly time-consuming. If you plan to tackle the issue yourself then a workshop manual or wiring diagram would provide useful guidance, but you might want to consult an automotive electrician for assistance.