Need Help. Picture.

[TimG]

This came out of the oil filter housing on my 90's style housing. Right at the back there is a plug and this went into it. What does this spring do? (My oil pressure light came on after I forgot to place it back in).

 

[TurboTerror]

There should be a single SS ball in there, like a ball-bearing, and that provides the resistance to create the oil pressure. You removed it and there was nothing to create resistance, that's why your low pressure light came on.