Trying to identify unknown connection plug
The part shown isn't a million miles for this 3 pin TE connectivity part: -



It's description on RS is: -


  Universal MATE-N-LOK Series 6.35mm Pitch 3 Way 1 Row Male Straight
  Crimp Connector Housing


You should be able to get the data sheet and compare dimensions. Then, when happy it matches, locate the female part.

You will probably find that Molex are an alternative supplier - I've seen very similar offerings from them.