There are 3 different color wires on the back of my cobalt oil pressure gauge, and was wondering which wire connects to the sending unit?

I do not remember the colors off the top of my head at the moment, but i should have the pillar off soon.

 

The additional wires are Purple, Black, and Grey.


The gauge already has power, so were trying to figure out which of those 3 color wires connects to the pressure sending unit