Several options here. You have a power antenna right? What energizes it so it goes up? You must have something there, you can use that wire to turn the basslink on/off. I find it also hard to believe that any deck would not have a 12 volt switched source, even the stock Bekker deck has one (for the antenna). You should re-visit the owners manual and look for a switched 12 volt lead from your head unit or look into what is powering the antenna.