Abstract: An oil pressure sender unit is disclosed which employs a two-part housing with a reinforced rubber diaphragm disposed between the two housing parts in order to isolate a pressurized oil cavity from a dry circuit cavity which contains the electrical components of the sender unit. In the preferred embodiment the reinforced diaphragm includes a peripheral lip which mates with a corresponding groove located within one part of the housing which is a metal base. The base has an axially extending inlet passage with a damper plug inserted therein which together defines a plurality of volume chambers that receive high pressurized pulsating oil at the inlet side and, because of its design, delivers a smooth flow of high pressurized oil to the underside of the diaphragm. This causes less wear on the electrical contacts that engage a two-sided circuit card which has a resistor circuit on one side and an on/off circuit on the opposing side.