So I recently bought this welder used. Longevity Weldall 250 Pi. Shortly after I bought it, the foot pedal quit working, so I took it apart, and found the rheostat was failed, no big problem. That is until I tried to find a new rheostat. I found one that was close, but while I waited, I was able to build a new wiper arm, and make it work. I have the new one now, but its working, so I will put it in later, it may add some more fiddling. Sorry I did not snap a pic at that time, but perhaps when I put in the new rheostat I will take it back apart and upload a pic.
So all is fine and well, but it frustrated me that I could not get an amp readout for max amps on the pedal while sitting static. With the pedal plugged in, it is just a garbage reading until you are welding. It is a little hard to see the readout when the lens darkens haha. I was also unhappy with the range of the pedal, so back in I went. I took the cog belt off, so I could get a feel for how it all worked, and started playing with the two rheostats, when I noticed that I could get the display to read what looked correct with both rheostats at full on, and no microswitch (switch open) the display showed 256 amps. So some more playing, and that was certainly the case, I verified it by setting with the switch open, and then close the switch and going full pedal, while watching the display. (that was tricky)
So experimenting was over, time to put things to use. I adjusted the pedal actuated rheostat so that I got full sweep from it when depressing the pedal. Then I saw there was an extra hole in the front board where the adjustment rheostat is. It was an exact fit for a toggle switch. I put a SPST toggle switch in the hole, and soldered one side of the microswitch in series, this when open will not start the arc, but with the pedal all the way on, you can adjust the rheostat so that it now adjusts the display to what max amps will be at full pedal. I am also quite happy that the pedal now has much smoother range as well, due to the adjustments I made.
So now with the new switch open and full on the pedal I can set the amps on the display, release the pedal, close the switch, start welding, and have the correct limit of amps as set, and I have great feel in the pedal.
Now for a pic, note the blue wires.
Now the next project, I want to make the pulse work with the pedal!
Many thanks to all the posts I have read here trying to figure out the pedal.