I wouldn't add any more lamp loads to the factory fog lamp circuit. You'd probably heat up the wiring, or worse, fuse the fog lamp relay closed.
The best way to do this would be to add a relay to the factory circuit so that the factory lamp circuit energizes the add-on relay coil and switches power to the fog lamps, maybe from the cigarette lighter circuit.
The best way to do this would be to add a relay to the factory circuit so that the factory lamp circuit energizes the add-on relay coil and switches power to the fog lamps, maybe from the cigarette lighter circuit.