If Tach is out-of-whack can it be reset?

I was going down the road and my windshield-wipers were slow. Then noticed Air-bag light on dash.  Then Air-bag and Engine light with Air-bag light going off. Shortly after car began seeming to stall and did. I was able to pull off the road and at this time noticed Tach needle was past all the numbers (7) and almost straight down. It has a stud at the Zero mark that it would normally rest on. I came to find that the nut securing the Alt wire was loose and it had a couple of electric bites on it and wire had come loose from connector at end of wire. I towed the car home, resecured end connector and replaced nut and all is well except for, now, the Tach needle is up against underside of Zero mark stud instead of resting atop it. Any cures? I appreciate your help in this matter.