Emissions Timer Resetting?

I found the emissions timer to my cherokee unplugged the other day, and when I plugged it in, the light came back on. I don't know if this is because it needed to be changed and the guy just didn't want to before he sold it, or it just wasn't reset or whatever. Is it possible to reset it or what? There was only one post on this and it wasn't mentioned in it, so I figured I would post this question. Thanks, Chris.

For the '87-'90s, the timer is a replacement part. You can't reset it. The '91s & up are resettable.

All it is for is to remind you to check your emissions. It is not directly linked to any sensor. If your mileage drops or it starts to run lousy, feed it a new O2 sensor. Otherwise, leave it unplugged and don't worry about it.