Volvo S60 2005 horns not working

Remove the wire connector from each horn and attach a voltmeter or test light. Have a helper push the horn button while you check for voltage. If there's no power getting to the horns you have to work your way back to the relay checking for shorts. If there is power try holding the horns metal mount against a good ground like an engine bolt or the sub frame. And with wire reconnected have your helper try the horn again. If it sounds then clean rust away from mounting bolt and car (rad support or grill bracket), and look for a loose or broken ground strap to the rad support (from either the battery or engine). If both horns still don't work either they're clogged with snow or dirt (bring them inside to defrost or clean out), or they need to be replaced.