When buying a adapter lead to change from a BMW plug to ISO connectors you have to make sure that all the pins are in the BMW plug. This is because some leads available on Ebay do not have all the pins and wires.
It may pay you to buy two leads and use pins and wires from one to fill the other.
This shows the BMW plug with all the sockets.
These are the connections.
This shows the ISO connectors.
Dave T