There are 2 ways to get oil pressure readings.
1. The preferred method is to use a galley plug replacing the stock sender. This is located under the alternator(the alternator will have to be removed & it isnt all that difficult). You will need a large size socket to get the stock plug off. If memory serves me right it is a 22mm.
2. Use a sandwich adapter on your oil filter to get readings.
Either way you have to run the wire through the firewall & wire the gauge to the fuse box inside the car.