Grounding Problem I think

[rushbuster70]

So my back tail light turns on but doesnt do anything when I brake.My turn signal also doesnt turn...They are on so I figured it wasn't a fuse.So I'm assuming grounding.Except for the fact that I don't really know what to look for.I know I should follow the wire harness but is there anything I should look for while following it?

Mucho Gracias in advance