[Mrmerlin]

swap the wires at the sender then you should see when you tun on the key the low oil pressure light illuminate and the gauge read zero before you crank it.
If you dont see these indications after swapping the wires then the sender is bad.

For the pin switch in the door pillar get a thin piece of wire and bend it into a hook slip it inside the pin hole and try to grab the wire you may be able to get to the wire by getting behind the carpet next to the hood release its a brown /white stripe wire