Switch works by breaking ground to shut off light. Remove switch from equation, if light remains on you have a short to ground somewhere in the wire that goes from switch to gauge cluster. Easy fix, run new wire. If light goes off, you either have low oil pressure or a shot switch, or one that works by the opposite principal as the one you need. Easy check, hook test light or VOM to switch body and wire terninal, see if its normally open or normally closed. Apply pressure where the oil would usually go, see if switch opens or closes. Start motor with switch removed to confirm oil pressure lmfao.