Quoted from wizardblom:
The other wire is soldered on the metal base making contact with the "spoon" (common), if I am not mistaken.
So that 2nd lug was not needed to make contact.
Maybe this will help answer some of your questions.
Your 3 Gottlieb pop bumpers all fire at the same time regardless of which one is activated, which means there has to be a "common" connection between them. So before you disconnect anything, locate and note the common wires.
I checked the switch stack config on my '76 Surf Champ (2 pops) and they match your old switches -- not your new ones. That's really weird because the 1978 GTB parts catalog shows PBR sent you the correct listed replacement -- part # B-17108/09 -- which appears to be the wrong part shown in the catalog diagram? IDK.
Keep in mind that the screws in these stack switches serve a true "electro-mechanical" function: as fasteners and as an insulated conductor through the switch body from the top leaf to bottom leaf. This should help you as you figure out your new connection scheme. (Both of mine have conductors soldered to each of 3 lugs with one wire as a the "common" carrier.) Be sure to double-check your schematic.