On most newer WMS/Bally games, the standard playfield coils have the hole
for a third (flipper-coil style) contact terminal on the plastic coil
bobbin. This comes in very handy to use as a strain relief for the thinner
solenoid trigger/return wire. Since the power wire is usually thicker, and
many of the assemblies hold the coils in a rather loose and floppy fashion,
it is common for the thin wire to break off from bending/shock. It is easy
to re-route the trigger wire through the unused hole and back to it's
terminal, thus preventing movement from bending the joint.