Volvo HU-603 audio does not turn on panel lights.

A customer brought me his Volvo HU-603 audio system because the lights on the removable front panel weren't turning on. He said it happened after hitting a bump. All the bulbs are OK. The Volvo wiring diagram shows that power is supplied to pins 1 and 2 via the Accessories terminal. But I think there must be another connection since everything else works except the lights. The LCD panel also works and its backlighting is fine... I'm lost...