The F-150 underwent a full redesign in 2004, and in 2005, Ford added the 4.2-liter V-6 as the new base engine. The oil pressure switch on the base V-6 is tucked away on the engine block, so finding it can be a little tricky.
The oil pressure switch on the 2005 F-150's 4.2-liter V-6 is on the driver side of the engine, directly behind the power steering pump.
