Front dashboard lights that shows the mileage gauge and mph dosen't work

You need to determine if the sender is bad or the gauge is. If you can get to the signal wire at the fuel tank for the gauge (this goes inside tank to sender that provides a variable ground circuit) ground that wire briefly to see if dash gauge rises. If so, part inside tank is bad. If not, gauge or some part of its wiring circuit is bad.

use your odometer. fill up tank, calculate mileage you can get on a full tank of gas.

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

several things could cause this, a connector on back of panel came loose, shorted wire rubbed through insulation. start with looking at gauge cluster panel.

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 gas gauge issue is the result of a defective gas tank sending unit.

do you have a dial switch to control the dashlight brightness? to make them bright or dim. i think that dial is all the way dim.

When the check gages light comes on just after start up usually one or more gages have momentarily not picked up yet. Dodges are famous for this. If the light stays on for more than 10 seconds and all gages are working t could be a faulty sending unit or you may have to get the computer software reloaded at a dealer

bad switch or fuse

Try to check the guage sensor in your tank maybe the contacts need to be checked or may be needs to be replaced...