Temp/MPG gauges inaccurate

[bizbquick]

I have installed an overhead console into a 2000 Dodge pickup that came out of a 1999 Dodge pickup. All of the wiring was an exact match and all of the wiring plugs in the 2000 were there. When the gauges were turned on, they worked but are not accurate. The temp slowly wanders ranging over 299 degrees and the mpg readings dont change or change extremely slow. Is there a small computer, relay, or other device that must be changed also? Do the gauges have to reset? A call to the dealer has got me no where, can anyone help?

[decmav]

having problems in instrument cluster on 96 1ton diesel, coolant temp running up to 190 and falling off to 140,oil pressure 40 falling back off to 10,volt meter increasing up to about 15,and fuel mileage went from great(22to24) to sh**.Batteries seem to be holding good, almost 13v with volt meter,and luckily have another oil pressure gauge in truck that's telling tha truth,coming straight off motor.That leads be to believe this is electrical, duh,but computer not picking up trouble codes,could this be sensor problem,or alternator going out,has anyone had a problem like this? Would appreciate any input,thanks

[kusterd]

If the truck does not support the new gauges I can't think of a good way to make them work. In other words the console you took out did not have the options that the new one does?