Got me on that one . . . I've never owned a turbo so I'm not too familier with its wiring schematic. However, you probably have a switch on the dash that allows you to turn on your fog lights on and off when you choose to. The non-turbo 700 series were not manufactured with factory installed fog lights so it didn't warrant having a switch on the dash.

I personally like the fog lights so I broke down and ordered all the hardware needed from Volvo and bought a used turbo front air dam and installed the factory fog lights onto my non-turbo wagon. However, when it came time to do the wiring I overcame the switch issue by simply wiring them directly to the low beams. I turn on the lights and my fog lights come on; hit the high beams and they turn off, and so on. What I ultimately lack is the ability to hit a switch and manually turn the fog lights off when my headlights (low & high beams) are on. A turbo may indeed be wired the same way that I have done mine but the major difference is that I can't turn my fog lights on and off via a switch on the dash.