I couldn't find the wiring design transmital for the 1998, but based on the 99.5 and my memory...
The cluster gets the vehicle speed from either the PCM (98.5 in Europe, later in the US) or a vehicle speed sensor. The cluster gets the fuel level signal from a different source. Assuming that you only have a single failure, the problem is internal to the cluster. Since the low fuel light goes ON in this condition, the cluster still has power.
Do any other lights come on when this happens? If so, the cluster is probably reseting. If not, you probably need a new cluster to fix the issue. However, there shouldn't be any drivability concerns, so I probably wouldn't go through the expense unless you have an extended warranty.
1999 Contour SE Sport MTX75 T-Red/Grey
Audio: Pioneer DEH-7400MP (MP3 CD), Pioneer TS-A6857 front & rear, PPI PCX-250, Infinity Perfect 10.1
Other: cup holders, cargo net, Blizzaks, Potenza RE950s
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