Hi can anybody help me, I have a 2008 focus zetec  the instrument cluster backlight wont come on but all the instruments work fine. I have changed the fuse but the problem persists. What could be the problem?

Have you turned the instrument cluster dimmer switch up to maximum brightness ?

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What do you mean by "the backlight"? The white LED gauge backlighting, or the backlighting for the LCD?

Which fuse did you replace? The cluster (at least the mk2.5 model) has three "power" wires (pins 4, 15 and 32), which pass through fuses F107, F108 and F114 respectively. Additionally power for white LED gauge backlighting comes in on pin 9 from the lighting switch assembly, which involves a dimmer switch (as unofix points out) along with a transistor (which I'm uncertain about), and can be traced back through fuse F103. However this circuit is only complete when the light switch is in sidelight or headlight position. This latter detail confuses me since if I go out to my car right now, leave the light switch in off position, and turn the ignition to position 2, the instrument cluster is illuminated, so I wonder if maybe the cluster internally turns it on regardless of light switch position during certain times of the day?

Just for fun here's a demonstration of power supplied on both pins 32 (on which power is normally supplied unconditionally), and pin 9 (illumination):

(Ignore the LCD, it's a dead one and is just sitting there to reduce glare from its backlighting).