In what part of the engine is the oil pressure switch located on a 1994 Cadillac DeVille?

My grandfather has a 1994 Cadillac DeVille. We're having trouble locating the oil pressure switch. He's had it checked numerous times at the Cadillac dealership. After driving for about 15 minutes, the light will come on and it says "Low oil pressure, please turn the car off". He's getting aggravated because the dealership says that nothing is wrong with it. We're going to change it ourselves anyway. Please help!|||Drive it into your dealership, when the light is on, and ask to have the oil pressure checked with a manual gauge.If ok(20 - 50 psi hot) tell them to replace the sender, while it is out. If you cannot locate the sender, I do not believe you will be able to master gauge the eng. to find out if you do indeed have low pressure, or a bad sender. It only takes 1/2 hour to do this, so wait for the car, if they can do it right away, otherwise take it back when they can do it right away.|||Oil pressure switch screws into the side of the engine right above the oil filter. Got to get under car to get it out. Just the other day at idle my oil pressure was at 8psi. I took a look under it and it had oil oozing all around it. It was very loose.