Get a schematic, Read Clay's EM repair site, then read it again. This is your bible.

Mid-1970's Bally you are going to find a lot of bad light sockets for sure. I would replace the garbage Bally fuse holders & check to be sure the correct value fuses are in it. Look at the large jones plug connector on the tilt board, you will likely find the connection with the green wire with the white stripe is burnt. Common on this era of Bally.

Fun pin, great backglass

Another thing on mid 1970 Bally pins. They used a common wire harness for the cabinet between several games, so you WILL find a few wires not connected to anything. This is normal, no need to panic.