Check to see if the battery leads have come off of battery terminals or the power switch.
If your light bar is equipped with a charging light, plug your light bar into the charger and verify that the charging light is lit and then re-test the switch.
Using a voltmeter, check the voltage of the two outer terminals on the power switch. If the battery is charged or is connected to your charge, the voltage should read 12 volts or more. If it does, turn on the switch and check the voltage of the terminal with the black wire and the center terminal. This should also read 12 volts or more.
If it reads 12 volts or more, the LED in the switch is most likely blown. This does not affect the operation of the light bar; it is just an indicator light.
If it does not, the switch is bad and needs to be replaced or there is a wire that is not connected between the battery and the switch. Replacement switches can be found at most electronics stores or by calling Custer Products.