Here is my setup for testing a VDO oil sender. I have used some brass plumbing stuff to connect the sender to an air chuck. I fill up a bicycle tire to a known pressure, then put the VDO/air chuck combination on the valve stem and read the ohms. I had posted this in the original forum a long time ago, and that time I had the sender connected to my MFD and was able to read pressure on the screen.
My original VDO has almost 400 hours and is still working - but I would see some pressure indicated after shutdown sometimes. Not sure if it was a sender issue, or a grounding issue. A poor ground would cause resistance and that could be why I was seeing pressure after shutdown. The VDO instructions say use no sealer on the pipe threads, because 1) that’s where the ground comes from and 2) what’s one more leak on a VW anyway? But I have been sealing it because I’ve not come to grips of the futility of keeping the oil in the motor. So I bought some 1/8” NPT nuts:
To make these work I had to run my pipe thread tap all the way through. But I was able to use it after to sock down an electrical lug to the body of the sender which I connected to ground.
I also bought an 1/4” NPT coupler and a 1/4” to 1/8” reducer bushing. My link shows as the 1/4” nut but it was 1/8”.