You need to download the FSM (factory service manual) PDF. The link is posted here frequently, but I don't have it saved. A search will find it.
For the specific oil pressure sender, the values are:
0 psi = 1 ohm
40 psi = 46 ohm
80 psi = 90 ohm
Make sure you are getting 7.5 volts to the sender. If not, you may have bad wiring or even a bad gauge cluster. Pull the connector from the sender and check the voltage.
Dodge did not build my Jeep.
1988 Wrangler,4.2L I-6, Carter BBD carb, 5 Speed Peugeot, Zone 2.5" lift + 1/2" booms, BFG 31 x 10.5, Bestop.