New defrost timer requires tap to start

My refrigerator has stopped running. If I tapped the defrost timer lightly it would turn on until the next defrost cycle (8 hrs). So I replaced the defrost timer with a new one but the exact same problem is happening. Any ideas what could be wrong?

Loose or bad wiring to it? Another bad timer? Its possible.

Thanks for your response. I just checked all the wires and they seem to be tight. I took off the back freezer panel to check thermostat and heater too. The timer is actually the 2nd new timer with the same issue.

Any other thoughts?