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The oil pressure light is designed to come on at about 5 pounds of pressure or five PSI. If the oil light is flickering that means you're losing internal oil pressure in the vehicle or the oil pressure switch itself is failing sending a fault signal. I have seen these switches fail. You have a couple of options. The first One is to simply by new oil pressure switch and install it. If the light continues to come on then you know you have an internal oil pump pressure problem. This can be due to a worn oil pump or excessive clearance in the bearings and camshaft journals. Your second option is to purchase an actual oil pressure gauge and screw into the hole after you remove the oil pressure switch and drive the vehicle to duplicate the problem and see what the oil pressure reading is at. As far as run on you need to inspect the ignition spark plugs and possibly doing a decarbon to make sure there's no carbon buildup on the cylinder head or piston themselves.

The oil pressure switch is located about four or 5 inches up directly above the oil filter and housing. It screws directly into the block. Three or 4 inches up and slightly to the right is the knock sensor. Do not confuse the oil pressure switch with the knock sensor. These are both under the intake manifold on the side of the engine block. It is almost directly back from the coolant pipe that bolts down to the side of the block.