Oil pressure sending unit

[captden]

Hi all: The oil pressure switch on my Ford Lehman stared to give me eratic readings and I knew the oil pressure was fine, so I replaced the sending unit on the block with a new 0-80 lb unit. Now when I first turn the key on the gauge needle goes all the way over to 80 lbs and is pinned there before I even turn the motor over. When I do start the motor, jt goes down to 40lbs and seems to be reading correctly as that was the same reading I had before this problem all started. When I shut down the motor and turn off the key it goes back to 80 lbs and then starte to drop toward zero. When I changed out the pressure switch I also replaced the gauge, I even tried the old guage and it does the same thing. I also have a alarm for low oil pressure that is wired to a different sending unit, and that is working fine. Anybody have an idea what is going on?
Thanks in advance
captden