gauge cluster 05 hemi magnum

I have a customer with an'05 Dodge Magnum with the 5.7 hemi motor and 160 mph speedo,problem: speedo and tach ..both analog are not working...now if i replace the inst. cluster from another car same model etc,and set mileage accordingly..will there be any glitches with the eprom as far as it coming from another vehicle i.e. starting accuracy,etc...thanx for all and any input.......phasephaseplasma

Are the gauges actually at fault? Older method. 3 on each. 12V+ Ignition. Ground. Tach AC from engine bay* Speed AC from g/box* *Measure each via DMM set to 20VAC, black to ground should get a 3-5 VAC reading on tach, rev engine it should increase slightly, speedo go from 0-5mph, should get a slight increase from 0-5VAC. If that's the case you're looking at power and ground, test. It just seems amazing to me that one let alone two would fail, never ever seen it. An 05 might even have the ins. panel as a complete processor, ground power and data being the only cables. For the second more likely method, I'd look at diagnostic testing possibly engine management.