db, most '98 cars are not pre-wired from what I understand, but that is really irrelevant since the OEM Volvo trunk changer costs over $400, wheareas an aftermarlet Alpine unit (model CHM-S620)works perfectly with the Volvo head units (with an adapter) and costs around $250 including the adapter and shipping. The Alpine unit comes with its own cable and believe me routing that cable from the head unit to the trunk is realy easy and requires no special skill or tools. For the actual mounting of the Apline unit in the trunk I used a bracket designed and sold by Volvo (P/N: 3533737, cost $12) vor the OEM changer. It took me about half an hour to make the Alpine changer mount to the OEM bracket and the bracket with the changer mounted to it screws into the trunk floor into pre-drilled and pre-threaded holes designed specially for that bracket. Rock-solid installation in less than 2 hours (this includes cutting the carpetting in the trunk according to templates provided with the bracket. Take a look at my install at the link below (I am in US, the site is not mine, but is a really good one).

Hope that helps.

P.S. There have been new changers branded by Volvo designed to go into the glovebox. They are really reasonably priced and come with everything you need for like $230. If you are willing to give up your glovebox, it's agood deal.