How can i solve the problem of reverse light on 2005 nissan micra 1.2 auto?

Hi, my reverse light went on my micra so i replaced it but it again blew straight away. After the garage had looked at it they cleaned the junction box (think thats what its called?) and it did work for 3 weeks but it has blown again and i woulf like to fix it myself rather than have to spend more money. Any ideas? Thanks, Sue