When multiball starts the general illumination flickers, a relay chatters, and then the GI and backbox lights go out until the game is power-cycled.

GI flickers and GI and backbox die when multiball starts: reflow the GI relay

Cause: Cracked solder joints on the pins of the GI relay (the clear 'ice cube' style relay), which lost contact under the extra vibration and load of multiball.

Checks

• Inspect the solder joints on the relay and nearby GI connectors for rings or cracks.
• Check the GI fuse clips are tight; push on the fuse to see if the clips are soft.

Fix

• Reflow (or remove old solder and re-solder) the GI relay's pins, and repin any burnt GI connector found along the way.

Systems

• Williams System 9

Games

• Space Shuttle

Related tips

• Rebuilding the +100 V section of the power supply
• Rebuilding the -100 V section of the power supply
• Score displays weak, dim or dead with fuses good
• Lower the display voltage to 91 V to extend display life
• Display supply low (under 90 V) after the resistors are changed
• Cross the legs when MJE15030/15031 replace SDS201/SDS202
• High-voltage supply rebuild parts, System 3 to 11C
• Fitting the high-voltage kit

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