Z4 headlight experts: Where is the ground terminal?

[Motionblurrr]

I think I'm getting unstable currents to my headlights (halogens) and I'd like to know where i can locate the ground terminal for the headlights are? Perhaps if I find it, I can see if it's corroded so I can clean it and re-adjust it.

my headlights are a very dim yellow compared to when I first got it they were very white. and yes I've polished the lenses and got brand new bulbs too.

any help? thanks in advance.

 

[bcworkz]

I think it's a little rectangular box on the side of either front strut tower.