A C-side coil or flash lamp does nothing in the solenoid test.

C-bank coil or flasher not working

Cause: Open bulb or coil, bad wiring, a bad shared driver, or the bank relay not switching.

Checks

• Ground the tab of the bank select relay driver (sol 12, or sol 14 on early games) and leave it grounded to hold power on bank C.
• Briefly ground the lamp socket or coil terminal, then the tab of that output driver on the CPU/driver board.

Fix

• Replace the bulb or coil, or repair the wiring or driver found faulty.

Systems

• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C

Related tips

• Whole groups of coils or all flashers dead: A/C select relay stuck
• Whole A or C bank of coils dead
• Wrong coils fire together (A/C bank game)
• System 11 coil outputs
• How the System 11 A/C bank select works
• How System 11 special solenoids work
• How System 11 A/C switched solenoids work
• Where the coil diodes are on System 11

Source: Pinball Machines: How They Work & Troubleshooting, Norbert Snicer