Pull 120 and 121 and turn it on, leave the game on for 5-10 minutes, see if it blows. Turn off, plug 120 and 121 back in, turn on, if it blows, you have a short happening somewhere on the playfield (this seems likely based on your background to me).

After you do what The_Director posted.

Things to consider - bad bulb, bad socket. Not always an obvious short.

When you do as he suggests, at least you narrow down some of it.

LTG : )™

Did you put LEDs in the Gis? It's very rare, but I once had an LED which had some internal issue and was causing my machine to blow the fuse related with that strand. After a ton of troubleshooting, I started to pull LEDs and finally discovered the cause was in one of the bulbs. After replacing the LED, all was fine.

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.

Do the coin door lights go out with that fuse blowing?

A bit of work unless you get lucky.

LTG : )™

Congrats! Light socket problems can be the most painful thing to diagnose.

The fuse #'s you got were wrong. I'm sure the reference is the CONNECTORs J120 and J121. These are for the GI string of wires, are on all the time, so if the game is on location - these were the connectors that always had current through them and they'd burn the plastic connectors. Also, the wires were too thin, and should have been a thicker gauge. I have redone my Addams with 18 guage wiring, new molex connectors and its working fine. It will probably never again get the stress of being on 12+hours a day, because it will probably never leave my collection.

Hope that clears up the references.