1) This is a sender for a pressure gauge, not an oil pressure switch used for an alarm.

2) Oil pressure senders and gauges were not standard equipment from the factory on most Catalinas, so you may need to add some extra fittings to the engine to install the oil pressure sender.

3) Regardless if you are installing an oil pressure sender or an oil pressure switch, never use any type of Teflon tape or pipe joint compound on the threads. The sender or switch are modulating the connection of the instrument to the ground by way of the engine block. If you insulate the threads, they can't make the connection to ground and the instrument will not function properly.