I spoke with my contact at Thule and the Thule Weekender box was never intended to fit on factory crossbars directly. So you will need to install a Thule roof rack on the roof rack of your 2000 Mercury Sable wagon and you would be able to use your Thule Weekender cargo box on your vehicle.
For a complete roof rack for your vehicle you would want Thule Podium Roof Mounted Foot Pack ,
Thule square load bar , Thule Roof Rack Fit Kit .
Once you have the Thule rack installed you would be able to mount the Weekender on your roof.
If you would like to update your weekender box to work on your factory crossbars you can use the TH04997 kit but some modification to the box may be required.
Are you a happy owner of 2000 Mercury Sable Wagon or just planning to buy one? Do you want to know more about your vehicle and technical specifications, its strength and weaknesses, to know the results of so-called SWOT-analysis, which is actually used in marketing however still applicable to any other situations? Some may ask without bias what they may need it for. I’ll explain.
Re:2000 Mercury LX Sable Stationwagon has a loud noise when turning corners, sounds like something is heavy is shifting in the rear of the car.
Also, the engine light is constant and flashes when stopped at stopped lights and shakes a bit at that time.
We took the car in for repair. One rear brake pan was replaced and one spark plug rubber gaget was replaced. The car's engine light went off for about a day but is now back on all the time.