After a playfield restoration everything worked except the number-of-players lamps on the backglass, which had worked before.

Number-of-players backglass lamps dead after playfield work: reseat the MPU plugs

Cause: A connector on the CPU (MPU) board had been disturbed and was no longer making good contact.

Checks

• Check every plug on the MPU board is fully seated and on the right header.

Fix

• Reseat the plugs on the MPU board (with the game off).

Systems

• Williams System 6 / 6A

Games

• Firepower

Related tips

• Tester LED check of the lamp columns
• Lights up but dead after storage: leaked batteries on the board
• Game keeps resetting: replace the 5101 RAM (an NVRAM works)
• Firepower CPU ROM configuration and jumpers
• What changed on the System 6A CPU board
• Reading the software ID in audit 00
• Seven-digit scoring on six-digit displays for green-ROM games
• Firepower original ROM layout and jumpers

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