Welcome to the forum!
Does the Odometer work (does it light up and change over time)?
The easiest thing to check are the fuses in the passenger side of the dash. Open the passenger side door and you will see the access panel. Specifically, check fuse # 29 (
see this page).
Both of these gauges get their INPUT signals from the PCM (computer) via a "Class 2" message (serial line). It could be a problem on the instrument panel, or even a loose connection going into the panel or PCM.
I take it you didn't get an extended warranty on it at the auction?
Take Care,