1987 excel green oil light stays light and yellow comes on between 3500 and 4500 rpm

[Cyachts1]

New to me, been running well and transferring oil to main tank. A few days ago I noticed yellow light flickering, and staying light 3500-4500 rpm. I filled the remote tank, but problem still there. the yellow light will go out under 3500 and flickers out over 4500. Any thoughts? I took sensor out of remote tank and cleaned. Since I cruise at 4000, I am concerned oil is not transferring. Thanks in advance.

[boats.net]

Need to test oil level sensor in remote tank and wiring between tank and engine.