Okay guys, how can i tell if my which tach is correct? My origional tach wire is spiced in with my new tach wire so i can compare the 2. Well they are almost 600-800 rpms off. Origional tqch runs 3000 on the highway new rach runs 2450. I idle at 900 on my origional tach and 600 on the new. Now lower rpms i think the new tach is right on but i hauled a** and on my origional tach i was about 4500 rpms and the new was about 2500 while i was accelerating. Sounded about 3000 rpms but i dont know? I can post a video tomarrow.