Sounds like the Service top half is okay.
The bottom half should be half lit like what you're describing.
There really shouldn't be any power going to it after completing one game.
The black or green wires in an IGT slot are normally ground wires.
All I can think of is a possible short somewhere maybe in that candle or the harness?
Braided wires should be grounded to cabinet metal.
You have to check around the connections.
That's a really old machine for one thing.... sometimes it helps to just unplug connectors and re-plug them back in to promote better contact, due to pin oxidization inside the connector housings.
If it turns out to be some IC circuit board component going out of specs....that's pretty much beyond my grasp because now you're talking about how to check individual components along that line.
That's where you need someone with circuit board sheets and knowledge of how to read them and test stuff directly on the circuit board.
The only fella I know that has that sort of skills or possess equipment to even check IC components would be NLG member Lookes.
Maybe you might want to get a hold of him and see what he can do for your board?