Theory of operation
The Elan IIE's remote cable release socket is a 2.5mm (submini) stereo socket. Plugging a 2.5mm jack into this socket gives access to three connections (tip, ring and sleeve).
The sleeve connection is a ground; shorting the ring connection to ground triggers auto-focus / auto-exposure, and shorting tip and ring connections to ground releases the shutter.
Because 2.5mm stereo sockets are small and not particularly robust, I decided to use 3.5mm stereo jacks/sockets for my remote, and use an adapter to connect these into the camera body.