[Lights fade in and out on start up]

It was the glow plug relay  bought another one and everything seems fine now thanks

[Lights fade in and out on start up]

Hi when I first start my car my interior lights and headlights fade in and out for around 10 minutes after that they are fine,the battery and alternator have been checked and they're fine could the problem be the ground cable from the battery to car body and could anyone tell me where on the body does it connect to thanks.  qashqai 2011 diesel