From Pinwiki:

If all of the controlled lamps are not working properly in the backbox, on the playfield, or both, this could be due to several reasons. Bad / marginal connectors, either on the rectifier board itself (male header pins) or the female housing that connects to it. A bad lamp bridge rectifier or blown controlled lamp fuse on the rectifier board could cause this too. The easiest way to determine if the controlled lamps are receiving the proper voltage on the playfield or backbox is to probe the bare controlled lamp bus wire (make certain to probe the controlled lamp bus and not the general illumination bus) on either or both areas with the red lead of a DMM. Then, connect the black lead of the DMM to a known, solid ground. Voltage should read approximately in the 6-8vdc range.

Additionally, if the +5vdc is missing on the lamp driver board, no lamps will light. Only one incoming pin (pin 3) on the J4 connection (upper left connection on board) of the lamp driver board carries the +5vdc. Check for the presence of +5vdc at TP1 of the lamp driver board.

Finally, the lack of a solid ground on the lamp driver board will also cause all lamps not to light. Most all of the different variations of the lamp driver board have the grounds secured via the screws which fasten the board to the backbox. However, the second generation of the Bally lamp driver board, the AS-2518-23, does not have these extra ground points. Since all of the lamp driver boards are interchangeable, there is the potential to have any one of the boards in the backbox. Pins 1, 2, and 11 of the J4 connection (upper left connection on board) carry the incoming grounds for the lamp driver board. The grounds originate from pins 3, 4, and 14 at connector J3 of the rectifier board.