After moving everything to a new playfield, the playfield GI doesn't work and its fuse blows, at first instantly and, after one wiring fix, a little later.

Playfield GI fuse blows after a playfield swap: solder blob shorting a socket

Cause: One GI socket had so much solder on its four-wire tab that it ran down and shorted to the socket base. A misrouted wire had also been causing the instant blow.

Checks

• Disconnect the GI feed wires to split the string into sections and find which section blows the fuse.
• Inspect each socket on that section for solder bridges and stray strands.

Fix

• Replace the shorted socket and resolder the wires neatly with less solder.

Systems

• Williams System 6 / 6A

Games

• Firepower

Related tips

• Number-of-players backglass lamps dead after playfield work: reseat the MPU plugs
• All controlled lamps out: bad spade connections on the bridge rectifier
• GI fuse glows and blows only when the playfield is lowered: bare GI wire on a screw

Source: Pinball Repair help group!! (Facebook group)