405 Estate late model - where do lighting earths terminate?

The reversing lights & read fog lights stopped working on the tailgate
of my late model Peugeot 405 Estate. I'd also noticed that the rear fog
light tell tale would light when in reverse.

I wasn't surprised to find that the earth wires on those lights in the
tailgate were floating - that is not connected to earth but only to each
other.

I have made a temporary fix, connecting the lighting earths to the
tailgate chassis - but I'm note sure the tailgate has perfect continuity
to the rest of the chassis. Without that my lights may be earthing
through some other connection & could just overload it.

Anyway, my guess is that the earth for those lights has come
disconnected at the other end of the wiring harness. Does anyone know
where that connection is though, under the steering wheel?

Regards