exterior temp reading wrong after replacement of display

[land sea air]

So here's my problem. I have a 1988 300E with the usual half broken exterior temperature display so I ordered a used one. Upon installation of the unit it is now reading about somewhere around 40 degrees to low of a temperature. Normally I would just assume it's the sensor reading wrong but before replacement the first half of the display would still be reading at least withing 10 degrees (ie it would be 95 outside and the display would read 9--- since the other half is broken) is there some sort of calibration I can do or maybe I have the wrong display? It looked slightly different in some minor ways but the part number was similar and it had the same plug as well as fitting with no problems...
Any ideas on this one?