Several lamp columns are much brighter than the rest in attract mode, some lamps stay on in play, and the large resistors on the lower right of the driver board run warm.

Some lamp columns over-bright: board or playfield?

Cause: Either a driver board fault or a short on the playfield (two column wires touching, a lamp diode shorted, or a socket shorted or wired wrongly).

Checks

• With the game on, unplug column connector 2J5 and row connector 2J7, leaving 2J4 and 2J6 in.
• Wire a single #47 or #44 bulb with two clip leads from one of the bright column pins on 2J5 to any row pin on 2J7.
• Still over-bright: the driver board is at fault. Normal brightness: two column wires are shorted on the playfield.

Fix

• Repair the board or find and clear the short.

Systems

• Williams System 3
• Williams System 4
• Williams System 6 / 6A
• Williams System 7

Related tips

• Match and player lamps light at random in play: faulty replacement driver board
• How the lamp matrix runs 6.3 V bulbs on 18 V
• Tester LED check of the lamp columns
• MOSFET lamp column upgrade
• Logic-probe the lamp columns and rows
• Lamp matrix column test at 2J5 with Leon's code
• Diode-test the lamp pre-drivers (2N6427/MPSA14)
• Fixing the burnt lamp matrix resistors R149-R156

Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Three, Clay Harrell (pinrepair.com)