Go look at every light on the playfield in that GI string. Inspect them thoroughly. Check for bent wire lugs that are touching each other or very close to touching (vibration might make them touch intermittently), a loose socket that is moving during the vibration of gameplay and touching something near it, any of the wires frayed or being pinched by another component near by, a wire surrounding any of those GI sockets that has come off another component and touching the socket. A solder splash on or inside the socket could do it too. Take out the light in each socket and really inspect the inside for any solder splash, metal shaving, etc. My buddy had that happen on his TZ and it would the GI fuse intermittently and it was very hard to spot the tiny splash of solder inside the socket deep in the cracks. If you have to, you can desolder each socket one at a time starting from the last one in the daisy chain and moving up the chain until it no longer blows. That's how I found his bad socket on his TZ....was very hard to spot, even knowing it was the socket causing the problem.