Sorry, but I don't understand. I appreciate that the clamp and tip swap polarity for the two modes, but I can't tell which lead goes to which.
I think there may be a misprint in the brochure.
For gas welding:
- red wire to post marked +ve
- black wire to post marked -ve
For gasless welding:
Just swap them over, i.e.
- black wire to post marked +ve
- red wire to post marked -ve
It couldn't be simpler!