Getting from car drop off at Basel airport (French side) to the Basel train station in Switzerland

The bus departs from the Swiss side of the airport. But it is only possible to cross from the French to the Swiss half of the airport inside the terminal. You need to do the following:

• Go into the terminal, and up to the departures level.
• Turn left and follow signs to the Swiss sector.
• You now are crossing a border INSIDE A BUILDING. There is usually no-one there to check you. See photo: https://static1.squarespace.com/static/513bcb31e4b0df53688faccb/t/56bcefa9e321405d05f97a27/1455222699337/image.jpg
• Go down one level to arrivals.
• There is an SBB counter in arrivals, they can sell you a Half Price Card, and tickets to Mürren which will include the bus.
• Go outside, look right, and you will see the bus stop. Get on the bus (green). See photo here: https://files.newsnetz.ch/story/1/6/7/16751284/8/topelement.jpg
• The bus runs every 7½ minutes, and stops outside Basel SBB station.

If the SBB desk at the airport is unmanned, just buy a bus ticket from the machine at the bus stop (you can see them in the photo), and by your Half Price Card and ticket to Mürren at the station. No rush, as there are trains every 30 minutes to Mürren, via Interlaken.

Thank you very much, Chris F. That's exactly the information I needed.