What's this?

[Major Fallout]

I have had the car for 3 years now, I still don't know what this little knob is?

Anyone?

[Major Fallout]

The very dusty one with the white dot on.

[A900ss]

Adjusts the time delay of the intermittent windscreen wiper frequency.

[Speed 3]

...or its the self destruct button....I dare you to rotate it

[QBee]

It's the "whingeing wife" button.
Pressing it ejects the roof 20 milliseconds before the passenger ejector seat fires.
You turn the knob clockwise for extra force if said wife is on the weightier side.....

[Major Fallout]

A900ss said:

Adjusts the time delay of the intermittent windscreen wiper frequency.

You're joking?

The intermittent wiper speed has always annoyed me! It's always been too slow.

[fog66]

Major Fallout said:

You're joking?

The intermittent wiper speed has always annoyed me! It's always been too slow.

He ain't joking, it's the wiper frequency adjuster for intermittent setting.

[Johnny 89]

A900ss said:

Adjusts the time delay of the intermittent windscreen wiper frequency.

I just went outside to check and it most certainly is. Although the fastest setting is still fairly slow!!