Instrument Cluster Malfunction

Dear experts:

Hope someone can help. These things cost $800 new at Performanceparts.com.

After I swapped a temperature indicate from a celcius to a farenheight on my
1984 300SD, something weird happened.

I don't know whether the problem was caused by above change.
In the Instrument Cluster
The Oil Pressure is ZERO, the DIESEL FUEL GUAGE, and Temperature is
at Maximum. Today's temperature in NYC is less than 45 F, so I know my
300SD cannot be experiencing overheated situation. And I remember
I had just a little over half tank, and I haven't driven it since I last looked at
that fuel level guage.

Can someone point me in the right direction ?
I have read in some posts on possible causes.
1. Fuse
2. Ground (but where do I look)
3. Loose power line behind the instrument cluster
4. Inside the instrument cluster, under the white paint ??, some lines
might have blown as a fuse would.

Any suggestions ?
Is it true the fue guage and temperature gauge would be maximum if there
was an unintended ground somewhere ? But where do I look ?