Before changing the switch please try to adjust the CNG Kit sensor. Its very easy.
i. Take a look at CNG Pressure Guage. e.g its showing 100 bar pressure.
ii. Loose two screws on the black plastic cover (land renzo only) just opposite to main cng input connection.
iii. Ask your buddy to take a look at Green lights on switch and keep on telling you the lights condition. Adjust the meter by slightly sliding the black cover. When 2nd green light go off stop moving black cover and tight the screws.
If CNG cylinder is empty and one green light is on.. slide the black cover till the red light turn on. Tight the screws.