Oil change boo boo

A little while ago I inherited a kz900. I discovered a oil leak where the wires come from the stator. The PO had purchased the new rubber grommet and today I installed it. Worked perfectly. I also decided to give it an oil change while I was there and did so. Upon restart the oil light did not go out. It has a oil pressure gage and it reads that the oil pressure is good. I installed the correct amount of oil. It has a Lockhart Oil cooler. Here is the part where I feel like a numbskull. As I was pouring the old oil into the recycle container I noticed a large flat washer in the pan. I know it is supposed to go on top of the spring before the filter but my question is is this what is keeping my oil light on? Like I said the pressure is good and there are no loud tickings so I believe the oil system is working. Can anybody explain this to me. I thought the oil switch was right after the filter or is my system bypassing? Going to fix the washer problem tomorrow anyway. Should I expect the light to go out?

i think the oil passes by the filter without tat washer, but its just my guess and the forum pro's will point you in the right direction.

No, the washer has no function other than to distribute the spring pressure more uniformly. Many are gone with no ill effect. I never bothered to replace mine after I noticed it missing some 25 yrs ago. I can't imagine how changing the filter could have caused a problem.

That washer mearly keeps the spring from pushing up, and possibly through the rubber grommet in the filter and preventing it from filtering properly.

Sounds to me more like some debris/sludge is possibly clogging the pressure switch.

Have you looked at the wire on the sending unit? maybe its going to ground or the sending unit just went bad