The light where the mileage and gears appear on the dashboard is out. Does the fuse have to be replaced? If so which one?

If the dashboard mileage light on your 2001 Buick Regal LS is very dim and the Service Vehicle Soon (SVS) light and antilock light stay on, there could be a few potential causes for this issue. Here are some things you can check:

1. Dim dashboard light: If the dashboard mileage light is very dim, it could be due to a burnt-out bulb or a problem with the dimmer switch. Try turning up the brightness using the dimmer switch, and if that doesn't work, check the bulb and replace it if necessary.
2. SVS light and antilock light: The SVS light and antilock light staying on could indicate a problem with the car's computer system or with the antilock brake system. It could be caused by a faulty sensor, a wiring issue, or a problem with the computer itself. It's recommended to have the car's computer system scanned for error codes to determine the root cause of the issue.
3. Battery or charging system: A weak battery or faulty alternator can cause electrical issues in the car, which could be related to the dim dashboard light and the warning lights staying on. Have the battery and charging system checked to rule out this possibility.

This is a common issue with this vehicle. The instrument cluster will need to be removed and either repaired or replaced.
If you replace it with a used replacement, you will not have your original mileage. I would send yours in for repair. Here is a link to a repair facility.
https://ricksfreeautorepairadvice.com/

You might want to check your fuses and possibly the wiring house. You could have a wire loose or possibly need ti replace the housing unit entirely.

Have someone check fuse under dashboard. Some dashboards have lights wired in series. If one light goes out, they all go out.

look for a 5-10 amp that runs the instrument cluster..

Still have same problem.

the first thing you should do is check the fuses, if it is ok, maybe the sensors need replaced.
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MVCI 3 IN 1

on many buicks and impalas there is a problem with the wire resistors falling off the circuit board! You will see four resistors upper right if any of these has fallen off they need to be replaced, Good news is you can replace them yourself ! go to your electronic supply store and buy 151 surface resistors and replace them ! These are 50 ohm and don't get hot and fall off. use a 15 watt soldering iorn. Don't want it to hot! Repace all 4 and wala it should lifgt back up! Douglas Noack texasinstrumentcluster.com

The odometer has to be pulled out. You dont mention what year it is, but double check your fuses to be sure.

it is a bad bulb or fuse check the fuse first since that is easier to do