Engine No oil pressure switch

I have a 71 baywindow us import 1600 twin port . I noticed it has no oil pressure switch in the normal place . there is no hole taped in the crankcase . the crankcase is a after market single relief valve . it looks new ish . on looking further I found a VDO oil temp sender fitted into the pressure relief valve There is a gauge but it doesn't look to be wired up . Can i replace it with a oil pressure switch and will it work the oil warning light correctly being under the relief valve