There should be 3 receptacles over on the left side of the fuse box that are marked "IGN". You can plug the tach power wire into any one of them. If you have the factory tach harness, it should already have a plug on the end of the wire that will fit right into one of those receptacles. If not, you can buy a plug that will fit them here -->
https://www.summitracing.com/parts/pco-0952pt?rrec=true