dummy guage changeover date?
http://www.ebay.com/itm/Ford-Instrument-cluster-voltage-regulator-5v-SOLID-STATE-LIFETIME-GUARANTEE-/281353725017?pt=Vintage_Car_Truck_Parts_Accessories&hash=item4181fd2459&vxp=mtr
You might also try to get a voltage reading at the sender with and without the truck running.
I have added some photos of what the oil press gauge needs to see across it, basically 2 to 3 volts drop across the gauge. The rest of the applied voltage needs to be dropped across the resistor in the sending unit.
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