Fuel Pump runs with key in "Run" or "Accessory position"

Older Chevy P 30 chassis that had dual tanks OR they had a vapor lock problem and the OEM installed a aftermarket fuel pump, they used one of the oil plugs at the oil filter block housing and installed a oil pressure switch that only when you had oil pressure would power be routed to the electric pump. Engine not running(no oil pressure) no fuel pump running. This is the easiest and a good safe way to power an Electric fuel pump. Doug