can you remove the factory radio on a 2000 mercury mountaineer and still use the controls on the steering wee

No you can not that do not work on any cars. If you remove the factory radio you cannot use the controls.

You can, l have a 2000 Mountaineer with an Alpine Navigation unit. What the guy when l had mine done 5 years ago told me was, they can do it on any stereo that has a remote control that u can use to control it. l think normal radio headunits would not work, but if u use a head unit that comes with a remote they can program the buttons to send the signal that would be coming from the remote. l seem to remember them saying they used some sort of intermediate box that learned the signals from both the steering wheel & the remote & then they spliced into the remote sensor.