I restored an old Trindle and found a Miller Electric Mfg welding service distributor very helpful. Miller has a real detailed parts catalogue. On page 8 of their 2000 parts guide is jack plug & receptacle parts Miller uses on their welding machines. It took a little sheet metal work but I was able to use their jack plugs and receptacles replacing all of the originals. I used the black, red, yellow, and white colored receptacles and set it up to show the stages of heat. Black to Black the coldest, Red to Red the second hottest, then Yellow to Yellow and finally the hottest, white to white. I notice that the catalogue that Miller doesn't show the white receptacles but your distributor may have them as a service repair item.
If you want to know what the amperage output is for each possible connection, the service distrubutor may for a small fee test your machine. They test all sorts of welding machines on a special machine called a "Load Bank". With this machine it will tell you what amperage and voltage is at each connection. Just write the values down and laminate with plastic and you have a good and handy guide.
You can hook up black to white, red to yellow, red to black as I did to get a variety of heat settings. Just remember one connection is to the electrode cable and holder and the other completes the circuit to the ground (work)clamp and cable. You can mix and match to get pretty much the control you want.
Hope this helps.
I have two more machines to rebuild like this one. One is a General Electric bought in 1947 or 48 according to the original owner. And the other is a P&H. Got them real cheap at an auction!