Is there any easy way to identify which wire under the dash is the one for the tach? I'm not installing an aftermarket tach or anything (yet) but wanted to make a little modification to mine. I'm going to put a little device in there to beep when I'm approaching a certain RPM, since I don't have a rev limiter yet (something else I intend to do at some point).

I autocross in my car, and do some road courses, and so I can't sit there and watch my tach to know when I need to shift and make sure not to over rev my engine =p

Thanks!