The oil pressure sensor switch in the 1985 Toyota MR2 is located under the engine cover on the passenger side of the engine, toward the rear of the engine. It is below the exhaust manifold and above the oil filter. If the oil pressure is too low or too high, the switch turns the indicator light on. If the pressure is too low, your engine will suffer damage. If the pressure is too high, it could cause leakage in the seals.
Locate the oil pressure switch in the rear of the engine. The switch is round and has one wire to it. Under the round top, you will find a hexagon so you can grasp the switch with a wrench.
Unplug the wiring harness connector from the switch. Fit the wrench onto the hexagon and turn it counterclockwise to remove the switch. The entire switch will turn. When it gets loose enough just unscrew it by hand.
Install the new switch by screwing it into the block by hand. Tighten it firmly using the wrench, but do not over tighten it. Plug in the oil pressure sensor switch wiring harness connector.