Not sure how the Rigid wiring harness is but if it has only power lines, you need to add a relay as explained previously and tap the Fog Lamp wire for the relay coil. If the harness has a switch and separate power lines, then the switch wire can be connected to the Fog Lamp and power lines to battery. Avoid connecting the power lines directly to fog lamp since it risks overloading the BCM which in a worst case scenario can fail due to this.
Thanks A.G this is really helpful , i also felt your idea of relay and wireless switch seems to be a better idea , without imposing any additional pressure on BCM. I would prefer to keep the rigid alone . Thank so very much again