Which earth for headlights?

[Mark.]

Noticed on a dark drive home the other evening the headlights flickered a few times. Was a bit worried they would just go out but thankfully they managed to stay working.
I'm guess the earth point is a bit dodgy so figured I'd give it a clean up - any ideas where to look?

[Tanguero]

Front drivers side of the chassis, down on the bottom rail.

[Mark.]

Thank you kind Sir.

Will pop down to the garage and take a look sometime soon