it could possibly be an issue with the difference between factory power and fog light power. i believe the factory lights are only 24 watts each, where these are 100 watts.
The harness makes it pretty easy, follow the provided instructions and instead of "switch" use the factory fog light wires.
When the factory fog wires have power, they will trigger the relay which will "open" the relay allowing power to go from battery through the relay to the lights.
When the factory fog wires do not have power, they will close the relay blocking the power from going through the relay to the lights