This is a great thread! Unfortunately it did not come up in search when I started diagnosing and repairing my module, so I had made a post about it and was directed here.
That dark/chrome spot in the glass display is normal, and is the result of the "getter" being fired during production to remove the remaining oxygen inside the display. You see the same thing in vacuum tubes, TV CRT's, and nixie tubes.
These are Vacuum Fluorescent Displays (VFD), and I believe those 510 resistors are part of its power circuit.
A bit about these resistors: the three digits represent a value and a multiplier. First two are value, third is how many zeros are after the initial value. 510 is a 51-ohm. 511, however, would be a 510-ohm, and a 514 would be 510K-ohm (510,000 ohm). The board connects these in parallel, which ups the wattage but halves the ohms, taking the circuit impedance down to 25-ohm. A single 25-ohm, half-watt resistor soldered to the pads is more than adequate and will get nowhere near as hot as the factory 510's did.
Keep this thread alive! As our trucks get older I'm sure more of these overhead modules will fail and this thread is a goldmine!
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