in front of the handbreak lever there is a connector for the switch that turns this light on. squirt some wd40 into the switch and check the connector is secure and the wires have not been pulled slightly out of the connector. there may only be one wire as this is a negatively switched setup.
in the lid of the break fluid reservoir there is a switch that also turns this light on. make sure its connectors are both clean and secure, and also take the lid off and push the float up and down a few times to make sure the switch's movement is smooth.