Most of the timers on older dryers are operated by a small 110 volt motor which runs thru a series of plastic gears and in turn rotates the timer cams inside the timer assembly. After a long period of time some of these plastic gears will wear out. Also inside the timer assembly the cams turn and move the contact levers to make and break the electrical connection. After long continued use some of these contact points stick or will fail to make contact preventing the electric power to flow. If your timer is bad and the dryer is very old it may be time to replace it as the cost of a timer is often quite high and not worth the cost of repair. An alternate p/n may work but you need to be able to match up ALL the connectors. I dont think you can buy a timer motor separate which means you must buy a timer assembly. If is is obsolete another Whirlpool model timer may fit and work.