Without first studying the schematic I would guess that the loose wire (black, w/ white stripe) belongs in parallel with the other wire (black, w/ white stripe) which is still attached to the coil lug.
Said another way:
Both of the black with white stripe wires should be soldered to the same lug on the coil.
If you look at some of the other coils - pop bumpers, drop-target banks, other flipper assemblies......you will probably find this same wire at each location. Said another way, the coils I mention will have two black w/ white stripe wires soldered to one of their lugs.
I hope this helps.
If you still need better advice - could you take a clear, hi-res photo of the schematic and post?
Ottawa, ON
