Quoted from PNBLWZD:Early solid state games sound great with a powered external sub, and even better if you can stick a small tweeter someplace. Early Bally games have a heat vent on the front of the head pedestal that is a good spot. I have this on my centaur and Medusa, and also just did black hole and haunted house.
I just use alligator clips connected to speaker wire to tap off the cabinet speaker, very easy and reversible.
What tweeter do you use - I'm thinking i could put one into the head pedestal of my medusa.