low oil pressure - sender wiring?

[Avantus]

Hi all,

I've got a oil pressure sensor that's reading up to 0.8bar lower on revs compared
with a mechanical gauge. I know these gauges are not te be trusted, but
the sender is new. The only strange thing is that I still sometimes have the needle
swing off the scale. Simply hitting the wires near the sensor normally makes the
reading work again. Now, could the dodgy wiring also have more resistance causing
the reading to be low, or do these gauges also go faulty?

Thanks!