In my V70 98, there are 3 yellow lights on the left side:

1) Tailgate door open: Usually does not light intermittently, it is either on or off.

2) Washer fluid level low: This can be intermittent when the level is just at the minimum, and you accelerate, turn or brake.

3) Bulb failure warning light: Monitors low beams, tail lights and brake lights. Right now mine is lighting intermittently like yours, but with a very consistent pattern: every time I press the brake pedal (and only when I do so) it lights up. And, obviously, one of my three brake lights is burned.

So the question in your case is: When does the intermittent thing happens ? When accelerating ? When braking ? Totally at random ?

Andy
(I bought the bulb yesterday, and will install it this weekend)