As with any locker (regardless of what you read, this includes Harrops and ARB lockers) some speed differential between the two sides being locked may be necessary to get the locker to engage. In the case of the CDL, this means turning while moving. It can take a bit of time for the splines to line up, because there isn't much differential between the two axle speeds even when turning. However, if one of your tires slips, the CDL will immediately engage, just like any other locker (Harrops and ARB's included). The confusing part is that the lights tell you when the locker has actually engaged, rather than whether or not the actuator is engaged.
Before swapping anything, try engaging it and turning a full circle. Also, if you don't have lockers and you verify that the CDL is in fact engaging, the light is only a convenience. If you have factory axle lockers, the light (or at least the signal to the light) is required for them to work. In that case replacing the switch is highly recommended.
As with any locker (regardless of what you read, this includes Harrops and ARB lockers) some speed differential between the two sides being locked may be necessary to get the locker to engage. In the case of the CDL, this means turning while moving. It can take a bit of time for the splines to line up, because there isn't much differential between the two axle speeds even when turning. However, if one of your tires slips, the CDL will immediately engage, just like any other locker (Harrops and ARB's included). The confusing part is that the lights tell you when the locker has actually engaged, rather than whether or not the actuator is engaged.
Before swapping anything, try engaging it and turning a full circle. Also, if you don't have lockers and you verify that the CDL is in fact engaging, the light is only a convenience. If you have factory axle lockers, the light (or at least the signal to the light) is required for them to work. In that case replacing the switch is highly recommended.
One thing to add is that the light will need to turn on if you want the ABS to turn off. When my Tcase CDL switch was non functional the CDL would still lock but the dash lights didn't come on and the ABS still worked. Having the ABS off is beneficial on dirt and gravel roads, at least in my opinion.