If it clicks only, the magneto does not engage properly. This switch has two functions:
1. engage the starter with the engine (like a clutch) - mechanical task
# provide high amp current from the battery - electrical task
# Often the magneto is rusted and does not move enough or its contacts are corroded.[br]
First line of defense: Use a hammer or heavy object to kick the magneto while cranking (2nd person required)[br]
You may use WD40 as well, should not harm.[br]
There is also another test that requires shorting/bypassing a connection. Requires knowledge and safety precautions.