Turn on the parking lamps... Walk around and see what works.. And what does not..
Then with the parking lamps on.. Turn on the hazards with the parking lamps..
If you have bulbs that go medium to bright.. You are ok.. If you find one or more that go medium to out.. Medium to out.. You have found a bad ground.. Either between the bulb base and the socket.. Between the socket and the wiring harness... Between the wiring harness and the body ground..
Since you neglected to post.. Year, make, model.. Almost all cars are wired in a similar fashion..
If you had a mid 80s Jaguar.. I would be having you do something completely different.