It started off when I bought the Rovair switch box from a seller in the states over 10 years ago.
It came as kit of parts that you build yourself. Some soldering is required from memory. It is just switches in a box with an EAS connector on one edge. The idea is that you unplug the ECU under the seat and plug in the box. It needs a jumper on the EAS relay as well.
It has proven to be a very useful piece of kit. It allows manual control of individual air bags and valve block. I carry it in my emergency kit box.
I took it a stage further. I bought a section of harness that goes from the ECU to the valve block so I can now use it on the bench to test valveblocks off the car. I fit a pressure gauge into each port and it is really easy to check if any solenoids are leaking. It is an absolute pain trying to sort out a problem with the valveblock on the car, especially if it is one of the solenoids underneath.
I have also connected a p38 air tank and compressor connector to it (switched via an old starter motor solenoid), so I can test air compressors easily.
It was actually made in Australia and I contacted the guy last year and he said he had not made any for over 10 years. No demand he said.
It would be a nice project for someone else to take over. I have a list of parts and a circuit diagram somewhere. It used radio shack parts which are the same as used to be sold at Maplin before they went bust. Only difficult part is sourcing the edge connector and getting the case molded and then printed.
I have got a 3d printer that could be used to print the case but if a suitable project box could be found that would only leave the EAS edge connector to source.