With LED GI fitted, the general illumination noticeably dims during play and even in attract mode, though the GI relay works.

LED GI goes dim during play: poor header on the interconnect board

Cause: A poor connection at one of the GI headers on the interconnect board (it had been repinned before).

Checks

• Measure GI voltage across each string's wire pair while it dims.
• Wiggle the interconnect board GI plugs and watch the lamps; look for burnt pins and cracked joints, usually on the right-hand side of the board.
• Rule out any GI power-saving or dimming setting in the adjustments.

Fix

• Replace the bad header and repin the plug (wiggling it only helps for a while).

Systems

• Williams System 11C

Games

• Diner

Related tips

• Dim GI and backbox lamps: GI relays swapped for boards that were miswired
• Rebuilding a burnt J6 GI connector: striped wires on the first four pins
• Flash lamp dead on an early System 11 game
• Lane change not working on Taxi and later System 11 games
• GI out on Banzai Run and later: burnt interconnect connector 2J6
• Interconnect board from another game fitted: the values Jokerz needs
• Two backbox GI strings out: the fuse was bad even though it tested fine in place
• The interconnect board (Banzai Run and later)

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