What is the function of this piece of the headlight lens?

 

if you are asking about the small dark triangular shape on the bottom left - that is the headlight washer.

 

Really. Didn’t know I had them. I’ll have to read the manual

Randy

 

I view them as bonnet/hood sprayers. I can see no circumstance in which my XK8 headlights are so dirty that they need to be randomly sprayed to reacquire function.

I've disabled mine since I kept accidentally 'improving' my freshly washed bonnet/hood.

 

My one set of headlights just had a plastic piece there and no washer assembly

 

That's best. I spent some time and effort making mine work only to find it distasteful.

 

I assume they come on when the windshield washers are activated. Is there a relay to pull that will disable only the headlight washers?

 

Generally, they spray every sixth time the windshield washer sprays. Remove fuse #7 (30A) in the engine compartment driver side fuse box (US) to render inop. If you prefer, you can remove relay #4 in the same box for the same effect. Should not affect windshield wash.