Where is the oil pressure switch located on 05 pathfinder

On my 05 Armada it's right in the middle, maybe a little less. If your using the right iul it should be fine.

by the oil filter,screwed into the block.

Oil level to low or it could be the oil pressure switch which is located in the engine block, remove the connector and earth or bridge the wire or wires and see if it extinguishes the oil warning light on the dash diplay.

According to my scanner, there is a crank sensor on the front of the oil pan , near the crankshaft pulley and another one on the oil pan or bellhousing facing the flexplate or flywheel...hope this helps.

If it's 4WD it recommends removing front gravel shield, and connector from oil pressure switch, then drain oil and remove oil filter. Then should come out top.

just above oil filter mount.

the pickup tube in the bottom of the pan may be plugged up.
Is the inside of the engine slugged up?
is the oil clean?
if it is dirty inside the engine, you can add a quart of auto trans fluid to the engine oil. it has a lot of detergants and can sometimes break up some sludge related blockages.
It is best to change the oil in a couple of days after adding the ATF
Another thing i have done to try clearing any blockage to the pickup tube, is to remove the oil filter and with an air hose and nozzle, blow into the oil ports and listen for bubles in the oil pan.
Just some ideas.

The low pressure switch in an A/C system cannot be manually "switched" on or off.
most A/C systems have 2 switches. Both of these switches are "switched" by the pressure of the freon in the system.
One is located on the high side of the system, and the other is on the low side of the system. The one located on the high side is a normally closed switch that opens the A/C clutch circuit and shuts the compressor off when the high side pressure gets dangerously high - usually around 350 - 400 PSI. This keeps you from having an explosion in the event that the hoses become restricted for any number of possible reasons.
The low pressure switch opens the A/C clutch circuit and shuts the compressor off when there is not enough pressure on the low side of the system to safely operate the system. usually somewhere around 20 PSI. The compressor is oiled by oil circulating along with the freon in the system. If the freon leaks out, the pressure drops and the oil cannot circulate because there is not enough freon to push it through the system. So the low pressure switch shuts the compressor off to keep the compressor from blowing up due to oil starvation.
Failure of these switches is very rare. Almost every one that I have replaced was not because the switch didn't switch, but because it was leaking freon.
If your low pressure switch is keeping your A/C compressor from running, it is most likely that the system is either out of freon (due to a leak somewhere in the system) or because it is unplugged.
Your Nissan is equipped with a "Dual Pressure" switch. it does the job of both switches by opening under extremely high pressure as well as extremely low pressure conditions. it is located beween the front grill and the A/C condensor near the Accumulator just to the right (as you are facing the front of the car) of the right headlamp area. See picture. To determine if this switch is functioning properly, you must hook-up an A/C pressure manifold gauge (to find out what the actual system pressure is) and use a volt/ohm meter to determine if the switch is opening and closing under the correct pressures.

there is an oil pressure switch that shuts the fuel off if the key is on and the engine has no pressure. the switch is useally located near the oil filter on the block, this is not a common problem so it is unlikely it is your cause of no fuel pressure.

their a red round circle that u pull on it just like the one from the oil exept the eng oil stick is yellow is usaly located close to the fire wall