Cut wires are common on these machines. They are usually on one or more of the coin unit relays. They haven't been used with coins for years. It's usually no big deal.
First thing I do on a Bally of that era is to replace the fuse holders. If they're not bad now they will be as soon as you remove and reinsert a fuse. After that check the connections at the Jones plugs. The Bally female connectors can be problematic. Then I would check all of the slam switches.
Move away from the coin stuff and the cut wires for now, and see if you can get it to light up and cycle by tripping relays manually. First press the Lock relay and see if it holds, then try things like the game over relay and the reset relay and see if anything happens. You can also try unplugging the coin door and manually tripping relays.
Everything you need is available here including a really cool color coded schematic that somebody spent a lot of time on: