Just tried to install a mechanical oil pressure gauge and having a problem.I put a tee under the oil pressure sender and attached the other end to the vacuum hose that goes to the gauge. The problem is that the vacuum hose going to the gauge is sucking up oil.
A better option if the gauge is installed in the interior would be to run an isolator, so no hot engine oil runs into the passenger compartment. They do tend to be on the pricey side, however. I think that's why most end up running an electric gauge.