To replace an oil pressure switch, drain the engine oil, remove the old oil filter and oil pressure switch, screw a new switch into the space of the old switch, and replace the old filter and oil. You need a service manual to complete this process.
Referring to the service manual, locate the oil pressure switch usually situated near or below the oil filter. To access the switch, put a collecting jar below the oil pan, open the drain pipe, remove the oil filter and allow the oil to drain.
Detach the connect cable from the switch, and peel off the rubber boot that cushions the switch. Wipe the contacts with a rag to prevent any future defects, and wrench out the switch. Using your hand, screw the new switch into the slot previously occupied by the old switch, and complete the process with a socket wrench to firmly secure the switch in place. Replace the connector, cover the new switch with the rubber boot and reattach the connect cable.
Apply the old oil onto the new oil filter's rubber gasket, screw in the filter with your hand and tighten it in place with an oil filter wrench. Cover the oil pan drain plug, and fill the engine with new oil, according to the service manual. Then replace the oil cap, ignite the engine and test the new switch.