Class 67 multiple working sockets

[RichardAsh1981]

Looking at 67 008 (my picture https://www.flickr.com/photos/30661871@N03/53923874619) I'm struck it has two multi-pin multiple working sockets on the end, as well as the RCH jumpers.
Old pictures of them in EWS livery only have the central AAR (Association of American Railroads) socket and the RCH jumpers, and online spec sheets only list the AAR multiple working capability.
What is the smaller socket to the right, with the label which says "Warning Do not couple or un-couple vehicles with engines running or battery switch in on position" above it? I presume it has been retrofitted at some point in the history of the class.

 

[sd0733]

Looking at 67 008 (my picture https://www.flickr.com/photos/30661871@N03/53923874619) I'm struck it has two multi-pin multiple working sockets on the end, as well as the RCH jumpers.
Old pictures of them in EWS livery only have the central AAR (Association of American Railroads) socket and the RCH jumpers, and online spec sheets only list the AAR multiple working capability.
What is the smaller socket to the right, with the label which says "Warning Do not couple or un-couple vehicles with engines running or battery switch in on position" above it? I presume it has been retrofitted at some point in the history of the class.

That's the 'Mk4 mod' and Is fitted to all the Tfw modified 67s (008/010/012/013/014/015/016/017/020/022/025/029) and allows a 42 way cable to be connected to the loco for working push pull with Mk4 DVTs and giving driver-guard communication and bell buzzers. It can be seen connected to the TOE of a Mk4 on this photo.

 

[RichardAsh1981]

Thank you!