I believe this is exactly the as fitted to Alvis Speed 20 models that used dual ignition. I has three positions, the middle for "Off" and one either side for either mag or coil. The spindle comes through the back to be connected to the H.T. change over switch on Alvises.It is marked "AM" under a crown but it is not an Air Ministry mark as far as..
New old stock 1920's American braided spotlight cable and fittings. There is a choice of two, as well as a NOS windscreen post bracket.$50 each.I can post these, and I accept PayPal.