I picked up an autometer ATM-1397 tach from Jason at Aplus over the winter an i am now trying to hook this puppy up. I haven't started yet, but i have the Autometer tach adapter aswell. I was talking with a very reputable person last night about it and he said i wouldn't need to use one. He e-mailed autometer awhile back and told him he wouldn't need to use one on his car but its a 96 grand prix gt which is already equpted with one. My car is not. So i e-mailed Autometer asking them what i should do so i don't void its warrenty. I personally think i need to use the adaptor.