I've decided to mount my mechanical AutoMeter oil pressure gauge inside my car is the isolator I will be needing?

 

it is not Nessesary to have that when installing an oil pressure gauge in your car. Its only nessesary with fuel. The only reason i would use it is if your worried about the gauge breaking and leaking oil into the cabin of you car. I use one of those on my fuel gauge and it seems to work fine.

Jeremy