Not an electrics expert but looks to me like it is on the ac side of things, so for ac mig?
Have you got a better picture of the whole front panel ? It could be for using flux core wire.
I know now that this connector is the earth for 'hot straightening'.
Probably something that would be little used but you never know.I just received a mail from kemppi with a scanned copy of the manual. Unfortunately the english part is missing. But I know now that this connector is the earth for 'hot straightening'.
I'll post more info when I can get my hands on it.