"the coil that never stops" is supposed to do that, it's the "coin lock-out coil" so if on location and no power to the machine, it will return your money
the back box buzzing I am guessing a stuck playfield switch locking on a either bell solenoid ( one on the match stepper ) and a score reel.
it sounds in a later post you may have remedied that but now the score motor keeps turning, manually reset all the score reels to zero, the ball count to 1 , player up to 1, all those steppers will need to be cleaned & lubed
from the video it looks like a beautiful machine.
Clay's guide is here http://www.pinrepair.com/em/index.htm