How do I set the correct gun polarity for different wire types on the Millermatic 350P?

The unit ships configured as Electrode Positive (DCEP), which is correct for solid steel, stainless steel, aluminum, or flux core with gas wires (GMAW). For gasless flux core wires (FCAW), you must reverse the lead connections at the terminals to set Electrode Negative (DCEN), making the drive assembly negative. Always read and follow the wire manufacturer's recommended polarity. (Page 15)