The level sensor is a switch, with a heating element attached. When you switch on, it gets 12V across one terminal and ground, which applies a bit of heat to a bi-metallic strip. If the strip is in free air (low oil), it opens the switch and lights the warning light.
Quoted resistance is 12 ohm...but not clear on which terminals that's between.
The pressure sender...resitance in ohms.
0 bar - 290 to 320
0.4 bar - 270 to 300
4 bar - 103 to 133
8 bar - 0 to 25
All figures for the 3.0 12V V6, but would expect them to be the same for all.
If your oil pressure gauge is reading low, it could be the sender diaphragm has sprung a leak and the casing is filling with oil. Take it out, then carefully(!) make a small hack-saw cut across the top edge (you are trying to make a small hole in the top of the casing - this method seems safer than drilling to me). Once you have a hole, turn it upside down and se if you get oil everywhere! If yes, re-fit the sender and see how the readings are now. If no, just seal the hole...and if possible, try another sender, or at least check it's calibraiton.