This board is called Flipper power supply. It makes power for the flippers and the other high voltage coils in the game.

Did you check for voltage on this wire?

Have you downloaded a manual, it will save you from following these wires thru the game as it will tell where they go.

https://www.ipdb.org/machine.cgi?id=804

Where did you find this black wire? Otherwise you can use the ground braid in the BB or cabinet.
Most of time the purple/yellow power wire is daisy chained from Line of Death Kickback coil. There is a lot of vibration on this coil and the wire may have broken off. This coil is on the top of the play field under a plastic. Give it a look see.

Check the voltage on the flipper coil. This will let you know if your meter is working or not.