Oil pressure gauge needle going crazy at idle

[MadrussianSVT]

After I changed oil to full synthetic T6 and attempted to tighten sending unit taped to oil filter housing I noticed that at idle my oil pressure gauge needle won't stay still, it's vibrating violently between 7 and 15 psi, it's all good wile under acceleration and this happens only at idle, why?

 

[obsidian]

Check the wire that connects to the sensor on the bottom of the oil filter/pump assembly. There should be two connections around there. Make sure they're clean and connected firmly.