The start switch on my Kenmore dryer was bad, causing the dryer to go into another timed cycle once it completed one cycle, and it would keep going until we unplugged it or left the door open. I repaired the switch at first, but after a couple of months the contacts bent again, so I just decided to replace it.
The new switch from PartSelect.com was only $8 or so plus shipping. Once I got the switch, I removed the rear access panel, disconnected the bad switch, and replaced it with the new switch. I closed the dryer up and it worked beautifully.
You can find detailed instructions on replacing the push-to-start switch on a Kenmore 70 series dryer on Fixya.com: