My clock would go on and off randomly until it just gave up completely. I identified that others has the same issues an indeed the clock just needed to be replaced. I thought it might have been a loose wire. I believe I had a hard time locating one if I remember right. Plus, I didn't want to pull my dash apart again with everything that's all set in there now. So I just use the clock on my aftermarket stereo.
Scott Yoder KD0DHP
2000 4Runner, 2.5" lift on 33's, locked, geared & armored.