Sbig ST-7-RC connector ST7

Hi

I have recently bought a secondhand st7 and have a connector labelled ST-7-RC that connects from camera to mount guide port.
My question is that this DB9 connector which has a phone connector at the other end also has a small wired connector sticking out of the side (whats this for??)
Appreciate any suggestions.

Attached Image:

One cable goes to the Filter wheel, the phone cord goes down to the "Autoguider" port on your mount.

Alex