So, after looking at the SP 125 Plus welder wiring diagram and corresponding with folks here I have come up with most of the parts necessary to build my own timing option. Using a kit from Velleman (PMK 111) will provide the timing. It has two adjustments: Pause and Pulse. The kit comes with pots that allow for a .5 to 5 second Pulse and a .5 to 60 second Pause. The Pause time pot is a 10 megohm and the Pulse is a 50k ohm device. Since the Pause pot has so much more resistance it is very hard to finely adjust. I will be replacing it with a 50k pot. In fact, I am going to replace both pots because the ones in the kit are trimmer pots and I want the adjustment knobs on the front of the welder. Whenever the the timer is powered up it pulses first so I'm going to wire the timer power to the trigger switch. The timer power comes from a 12 volt 200 ma wall wart. By using a double pole/double throw switch the timer can be totally isolated from the welder even though the trigger in the handle will be the on switch for it. So the welder will have a switch on the front that can be set to either CONTINUOUS or STITCH. Manually stitch welding a few minutes ago I discovered that the Pause time should be independent of the Pulse time. What I can't tell easily is how long either should be and what would be the minimum and maximum times. The timer should be made such that it has enough range without having too much so that it is easiest to adjust. I think the Spot timer is for plug welding. By Plug welding I mean that one piece of metal has a hole in it. This piece of metal is clamped onto another piece of metal such that the hole is blocked at one end. Then the hole is filled by welding. I hope I'm using the correct nomenclature. Please feel free to correct me. Since the Velleman timer uses higher resistance to increase the Pause time, and since it resets every time the power is removed, a switch which disconnects the pause pot will allow it to weld for a set time and then turn off until the power is toggled. Anyway, here are the questions:1) What is the minimum Pulse time. 2) What is the maximum Pulse time. 3) What is the minimum Pause time. 4) What is the minimum Pause time. 5) What exactly is the Spot timer meant to be used for when the timer is the one provided by Lincoln. I called Central Welding, where I buy most of my welding supplies, and they hadn't even heard of the Spot/Stitch timer kit for the SP125, or the SP135. So they couldn't tell me what the Spot setting was for. And Lincoln doesn't sell it anymore. There must be someone there who knows the answer but that someone wasn't at the Lynnwood store today.
If anybody wants me to I can post a parts list and wiring diagram when I'm done and it's working correctly.
Thanks for reading and responding, Eric R Snow