How a Harley Davidson Oil Pressure Switch Worksby Chris Gilliland
Harley-Davidson's motorcycles come equipped with an oil pressure switch and a corresponding indicator light to provide the rider with a visual warning of a potential problem with the engine's lubrication system. The switch itself is simple in design, but it can play a large part in your motorcycle's overall health.
Oil Pressure Switch Construction
The standard Harley-Davidson oil pressure switch resembles an enlarged bolt with a larger-than-normal head, from which extends a pair of wires. Within the sensor's threaded shaft is a pair of electrical contacts that form a normally closed electrical circuit at rest, meaning the circuit is complete to allow the oil pressure light to illuminate. One contact is affixed to the shaft, while the other can move along the length of the shaft. A spring is used to keep the movable contact against the fixed contact while the engine is at rest.
How the Switch Works
On a stopped engine, the oil switch contacts are held firmly together, which illuminates the low oil pressure light on the motorcycle's instrument cluster. As the engine powers up, the oil pump pressurizes the engine oil and forces the switch's movable contact away from the fixed contact. This breaks the circuit and turns off the low oil pressure light. The switch requires very little pressure to keep the movable contact in the open position, as evidenced by the 10 pounds of pressure generated by the engine at idle. But the contact will close and complete the circuit if the oil pressure drops below 5 pounds per square inch.
A low oil pressure warning can be triggered by several conditions within your motorcycle's lubrication system, but not all of them are cause for alarm. This first thing to check is the oil level in the oil tank; an insufficient oil supply reduces the amount of oil circulating throughout the engine. If the oil supply is sufficient, check that oil returns to the tank from the oil pump. If the oil does not return to the tank, the oil lines may be clogged, the oil relief valve may be stuck or the oil pump might be damaged internally. An oil leak might be present if oil is returning to the oil tank, reducing pressure as the oil bleeds off through the leak. If all of the conditions appear normal, the oil pressure switch itself may be at fault.
Oil Pressure Switch Replacement
Assuming a full supply of oil, the oil pump works properly and oil returns to the oil tank, the oil pressure switch may be stuck in the closed position. The oil pressure switch is on the bottom of the oil filter mount or the left-front side of the engine crankcase, depending upon the model. A special socket is available from Harley-Davidson for removal and replacement, but an adjustable set of locking pliers can be used in a pinch. Once the old switch is removed, screw the new switch into place and tighten it from 96 to 120 inch-pounds with a torque wrench.