If you're looking to add a tach wire to your alternator, there are a few things you'll need to keep in mind. First, you'll need to identify which type of alternator you have. There are two main types of alternators - those with internal regulators and those without. If your alternator has an internal regulator, you'll need to remove the regulator before proceeding. Next, locate the two large terminals on the back of the alternator - these are the battery and field terminals. The tach wire will be connected to the field terminal. Finally, use a wrench or pliers to loosen the nut on the field terminal, insert the tach wire under the terminal (making sure it's making contact with the metal), and then tighten down the nut again. That's it! You should now have a functioning tach wire on your alternator.