Bilbo, you are experiencing a very well known problem. Here's the deal. Your front right turn signal bulb has collected some carbon on one of its terminals due to arcing. The style of bulbs chosen for that particular light assembly was incorrect for this application. Too much current and not enough contact area produce arcing and carbonizing of the contacts. You can fix this by simple removing the bulb and scraping the carbonized contacts of the bulb and the socket clean with a small Swiss army knife (it will be obvious which contacts need attention). I usually then rotate the bulb 180 degrees so that the second contact is now at the arcing side. This gives me at least 6 more months of service out of the same bulb and socket (actually last time it held up much more and was still good when the dealer replaced it via recall). Volvo does have a Volvo has a recall for this problem, where the sockets and bulbs are replaced with a different design. To me this was never a big enough deal warranting a recall, especially when there are bigger fish to fry for Volvo like AC evaps and keyless entry receivers. Oh well, cheap fix and good PR, how can Volvo go wrong?

Good luck.
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Vladimir. 1998 S70. Base, 5-speed manual.