The old style flashers use a bi-metallic spring with contact points. when cool, the spring closes the points.
When you complete the circuit via the TS switch the current flows through the spring to the contact points. The current passing through the spring heats it up and causes it to spring open (TINK) and breaks the current flow through the contacts When the spring cools it closes the points again (tink) and re establishes current flow.
As previously mentioned you most likely have a bad flasher
Note that using LED lights will not draw enough current for the old style flashers to work.
Also note that a burn out bulb or bad ground can also cause problems as either can affect the amount of current passing through the spring thereby altering its "timing"