12v is supplied to the lamps themselves through the 2.2 ohm resistor on the lamp board. You should see 12v at pins 5 and 6 (that goes straight to the bulbs), then the grounds are controlled through the uln2068s. That resistor (R19) is famous for opening up, and if there's no current through it (ie, the cpu isn't calling for lights), unless its completely opened, you will see 12v there, but, when the uln2068 completes the circuit, there's so much resistance that the bulb doesn't illuminate.
Long story short, i replace that resistor (R19 2.2ohm, 1watt) with a 2.2ohm 3w resistor on every lamp driver i work on. Its overkill, but its one less problem it'll ever have again. You can bypass the resistor temporarily by putting a jumper wire across it. Don't leave it that way, as that resistor is there to dim the bulbs a bit to keep the heat down and the bezel from flaking. If you bypass R19, and the lights work. Its R19.