This sounds like what my dad bought back in the day for our dogs. It killed a full grown rabbit once, and my dad somehow toned it down but I don't know how he did it. I wouldn't use it around cats...
My dad had a lightbulb with two wires. One on the ground, one on the hot wire. If I attached it, turned it on, and it lit up, then the fence was working. If it didn't light up, I had to go figure out where it was grounded out.
My dad bought one intended for horses and somehow turned it into one for dogs. (He worked on equipment and such so he knew what he was doing.) I forgot to turn it off before feeding the dogs once, and when I leaned over the fence to give a treat, it got me and bit my dog (who was taking a treat...