I recently picked up a Sovtek Mig 100 from a local guitar store. The Sovtek was sold without the pilot light in it. I'm not familiar at all with schematics, or even the term "pilot light" but I heard that is what they are called. From the looks of it, all I need is the lamp to click into the input.
hard to say if that lamp will fit in the bulb socket or if that's even the right type. you might have better luck ripping out the original pilot light assembly and putting in a new one. replace all the plastic jacks, pots and switches while you're at it as well.
It's probably just a standard 6v filament bulb. Is the inside socket still there? You could probably email New Sensor who bought sovtek and ask them if you want the exact one and/or a replacement lens.