HELP Oil Pressure gauge install???

[juls213]

HI I bought an oil pressure gauge from a member. I want to know how to install it. I installed it already but it is giving me the wrong readings. Its a 4 wire system. Here is how I installed it
red : 12v source voltage
black: Ground (-)
purple: 1 wire going to electronic oil pressure sensor
orange: ?????

What is happening is I am getting 60 psi in the highway and 0 at idle, but the weird is in the highway the 60 psi would change when i turn on the light the psi goes down to 50, then I put on another load and it goes down even more.

Can anyone tell me how they wired their oil psi gauge, thanks