[Roadtrip]

The sending unit on the filter housing is for the light. The gauge sending unit is on the rear right side of the engine. It's possible that the gauge sending unit is defective. The light sending unit is simply an on-off grounding type switch that you can test with a test light. One lead to the + battery and the negative to the tang on the sending unit. If the oil pressure drops below 5 psi, the switch ground and turns on the light.

Never start tearing down an engine for oil pressure without check the exact pressure with a direct read gauge. Alfa gauge sending units are notorious for going bad.