04 Mach1 instrument cluster lights not working

Confirm fuse F2.37 is good. Confirm there is power in and out. Use a known good ground and ensure that the head light dimmer switch is turned all the way up. Not a bad idea to double check that the voltage at fuse F2.37 changes when the head light dimmer switch is rotated. This will confirm that the dimmer function actually works. Even better. Confirm with a test light that will LOAD the circuit.

Confirm that the illumination lights work at the other locations such as automatic transmission PRNDL. Even better to confirm that the other illumination lights dim or get brighter as the dimmer knob is turned up and down.

When power is confirmed at fuse F2.37 then check the cluster grounds. These will be the black wires and the black wires with white stripes. Best to confirm a good ground all the way back to battery negative.

Note, the cluster is grounded behind the center console. This ground is shared by multiple devices including the radio. This ground is frequently messed up during a radio install.

Disconnect the cluster edge connector. Is it clean? Any evidence of corrosion? Inspect the copper printed circuit foil traces. Any evidence of wear?

Finally. It is possible for the light bulbs to just burn out. It will help to pull the cluster and inspect on the bench.

Check out this thread on Cluster PC foil trace repair.
https://www.allfordmustangs.com/forums/v6-tech/304608-my-odometer-goes-off.html#2657361

1999-2004 MY fuse panel schedule:
https://www.allfordmustangs.com/for...r-swap-wont-fire-please-help.html#post2669271

Here's some information on how to test the quality of a ground all the way back to battery negative. This is the "acid" test for any electrical circuit path.

Howto perform charging system voltage drop test
https://www.stangnet.com/mustang-fo...perform-charging-system-voltage-drop-test.56/