Yes, there are multiple bulbs. 5 of them, 1.5v each.

First I've heard of a cluster-only light sensor, I doubt it.

There is a cluster brightness rheostat at the light switch, above the fog light switch. Only works when the park lights/headlights are on.

First I've heard of the disconnect battery for cluster problems. But that has been suggested for lots of other things, sort of a cure -all lol! I dont think it will hurt anything to try.

Your problem sounds like a few bulbs out. I would be inclined to start there.

If your info display and selector position display still light up, you can swap bulbs from there to the non working areas to test.

It's real easy to pull the cluster, it's just the two screws, then lever it out from the top. Just adjust the column down and forward for space.

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04 X5 3.0i auto
03 X5 4.6is