installing Tach, no previous tach

[Pimpin Dsmstyle]

This is a honda civic 91. The car did not have a tachometer and we have decided we are putting one in. My question for someone like Eric, how can you wire this up when there is no tach line to tap into? Everything else is wired up and mounted, now it is just this "green" wire that we have no idea where to put it. Thanks for the help if anyone can!!