Klaus, you're my hero, you and others on this site have really helped me out since I bought my 04 S60 (NA) and realized I'd go broke if I had to take it to the dealer for normal maintenance and repairs. I really like the Volvo, but they do have some "Swedish/Euro quirks" which are fun to figure out. Like the "Position Lamp Failure". I eventually found that the "Position Light" isn't what someone in North America would call the parking lights, nor the brake lights; but a separate, stand-alone light which is supposed to be used as a sort-of reverse fog light. I think the idea is you're supposed to turn it on when its foggy so people behind you can see you better (or maybe you turn it on so people can see that you've pulled to the side of the road). Whatever the original intent, it's a separate lamp, above the brake light lamps, in the red lamp housing, and on my '04 it's on the left-hand side. There's even a button on the console with a universally easy-to-grasp symbol which clearly shows what this thing is for, and does. Needless to say, 4 years after we bought it my wife and I finally figured out what the postion lamp message was for, and that the bulb needed to be replaced. I definitely agree that when replacing brake lights, headlights, or parking lights, you'd better replace them in pairs. But there's only one Position bulb, and it's only on one side. Have someone step on the brakes, make sure both brake light bulbs on either side are OK, then open the trunk, look near the brake-light assembly, and find the extra position lamp bulb. With the key on, press the position-lamp button, see if it comes on; if not, replace.
Hope this helps.