The front brake light switch is not adjustable. There are a couple of things you can try though.

First check that the switch is mounted solidly and isn't moving in its housing. Particularly check the retaining pin/clip, which can get sloppy over time. Also check that the actual lever pivot hasn't got too much play in it because that can cause poor brake light operation.

Next try using contact cleaner (or alcohol based brake cleaner), squirting it into the the gap around the plunger (you might be best removing the lever to gain access). Push the switch in and out, spray some more and keep repeating. This may bring the switch back to life if it's dirty contacts causing the late operation.

If that doesn't work you can cut/nibble a bit of the end of the plunger, so when you pull the lever the plunger starts to move out earlier.

Failing all that you may have to resort to a new switch, they do wear out and are exposed to a lot of road spray and damp. They aren't expensive, I think they are about �15 (18 euro). However, as long as it operates (however hard you have to pull the lever) it is legal.

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