Cadillac Repair: Fuel econ display in metric, plastic connector, climate control

Question
I have a 1985 Fleetwood with the 4.1 V8 FWD.  It has the fuel econ display and tells average mileage, fuel remaining in tank, etc...  The problem is that it only displays this information in metric units of Kms and Liters.  I know there are two versions of the dash for this vehicle, one has a switch to change between english and metric, one does not have this switch.  I unfortunately do not have this switch on my dash.  Is there any way to make the display show english units?  Is there maybe a button combination like the error code readings you can get through the climate control?  Any help would be greatly appreciated.  I would really like to know how many gallons of gas are in the tank as well as how many MPG I am getting.  Thanks for your help.

Answer
is the speedometer cluster DIGITAL ?. Or has it been replaced ?.

There were 2 versions one with a metric/english switch and the other style was there is a wire that comes off one of the computers that has a GREEN plastic connector that is tied to the wiring harness and if grounded changed the displays.