Are you sure nothing is shorting under the playfield?

There is one GI light socket that has a habit of shorting out. Its near the top of the left playfield support. From vibration the lamp socket will touch that support causing a ground short.

J120 and j121 are the same connectors. Pull them both and verify you fuses stop blowing. If they blow, issue is in the board. If they don't blow, issue is probably in the wiring. If you're worried about the bent pin, you can uh the j120 connector into j121 and leave the back box lighting off. Does it blow a fuse? If so, issue is in the wiring or sockets. Exflexer probably is in the right track here.

Pin 4 is the keying pin. It should be cut out.

Definitely check the GI socket near the playfield slide. That has caused problems on many machines.

I had a similar problem with the upper GI on my whitewater also.

One thing you can do in the future is unscrew all the sockets on the GI string in question.

Lets assume at this point there is no problem on any board.

Put in a fuse, and if it blows, it could be one of the sockets shorting, but this is a good indication that the short doesn't involve something contacting the sockets on or below the playfield. If it doesn't blow, it is a good indication that the short is caused by contact with some palyfield structure.

Next: if it blew, remove all bulbs, replace the fuse and one by one replace the bulbs. if it blows again you have identified the problematic socket. If it doesn't blow after the last bulb is replaced, then begin to replace the sockets in the playfield one by one until the fuse blows. If it doesn't after all this, jiggle gently or tap gently on each socket in place and see if you can cause the fuse to blow.

If this process has not found the problem, then it probably is not in the string I would think. Take a break, get a beer before you yank the GI out of the game.

Glad you got it working. I remember that had me scratching my head for a while.

Dan