Renault Megane 53 plate (Dynamique)?

Does anyone know if there's anything about bad earths in the Megane? Where they are, what they look like n how to fix em if poss?

Our problem is the front left indicator doesn't work and changing the bulb hasn't remedied it. The rear light on the right only partially lights up the filament - very strange. Had both rear lights off and replaced the rear fog light. Then changed over the light holder one from the other side of the car but it was still the same. So it's not the bulbs or holders at fault and must be a bad earth somewhere - I think anyway? Inside the car, the passenger airbag light is constantly lit.

We had a major problem with the fuse box following a particularly long trip in rain, and had to have the fuse box replaced. The above problems have occurred since then.

Would really appreciate any help or advice.

Thanks