hello there chaps

i have bought myself a syil c6 with mach3 and have just about found a home for all the plugs etc.......except one

it comes from the back of the syil cnc controller but i cant find anywhere on the machine where it should plug in

the chap i bought it off said it should plug into the headstock but there is no socket there

ive added a couple of pics of the machine , controller and offending plug in the hope someone who knows what they are talking about will see the plug and know straight away where it should go...???

maybe it shouldnt plug into the machine at all but maybe the pc...??

thanks for any info