2003 MCS, Kept getting intermittent oil pressure light when coasting on the freeway but would go away as soon as I tap the gas. So I had the recall service done for the power steering pump assembly and fan and now my oil pressure light is always on. The engine purrs like a champ so I went and replaced the sender to no effect. Then decided that I might as well pull the actual oil pressure so I grabbed a BOSCH gauge kit from the Advance Auto shelf and threaded it in - even with my leaky install I got 60PSI upon start that tapered off as the initial start rpm's settled.

Now, my sensor is no longer plugged it - just an analog gauge directly to the sender hole. My oil light is not on with the sensor unplugged. I thought the behavior should be opposite as the sensor missing = no pressure = dash light. I am experiencing the opposite and obviously I have the correct pressure. What am I missing ?

 

You've got it backwards. The oil pressure sender grounds the circuit, and is normally closed. Oil pressure keeps the switch open.

I've got the same problem with my car. There's an intermittent ground fault in the circuit that makes the light go on and off as the engine rocks back and forth in the mounts.