Hook a multi-meter to the sending unit and measure the resistance between the pin and the engine block / ground. You should be able to see a change in resistance with the engine running vs off. Also, see if you can measure the resistance on the old sender (if you can put a probe on whatever is left of the post).
Applying Murphy's law, don't be surprised if the situation is: Sender type 1 - minimum / zero resistance at zero pressure, max resistance at max rated pressure Sender type 2 - minimum / zero resistance at max rated pressure, max resistance at zero pressure > The last time I ran my engine prior to making a new starter mount / housing, my oil pressure gauge was working perfect. To remove the old starter mount / housing, I also had to remove the oil sending unit. Therefor, I disconnected the wire at the sender. I noticed in the mean time as I was working on my plane, if I turned the ignition to on, the oil pressure gauge would max out. I think this is normal with the sender disconnected. Anyway, I reinstalled the sender after I made the new mount / housing. I then went to attach the wire and twisted the post right off. Bummer.... I ordered a new $35 sender and it arrived today. I installed it, attached the gauge wire, turned the ignition to on and the gauge immediately maxed out. What's up with that. Is it possible the new sender is bad? Is there a way to test the sender? >
