This Spool Gun is outfitted with a 5 pin connection unique to Metal Man Multi Process machines.
Sorry for the slow response. We highly suggest that you contact your local Weldmark dealer. There are two different versions of the Weldmark MIG 25-140. Check with your local Weldmark dealer to be certain. www.weldmark.com
Thank you for your questions. We are not familiar with the spool gun requirements for the Harbor Freight Models. It is likely the 5-pin connector is a coincidence and it should not be assumed that the connections are the same. The dc voltage range in order to run the spool gun at the required speeds are likely different. Our spool gun also uses a separate quick connect for shielding gas pickup.
I am sorry, but the MMWM142i does not have the internal circuitry to support a spool gun.
Yes this Spool Gun will work with the Metal Man MP140T