ok so im swaping over to a mech. oil pressure guage and a mech. water temp guage cuz mine keep acting weird. my question is can i just remove the old sending unit and thread in the line to the new guage or do i need to add a t and keep the old sending unit its a 92 with a 4.0

 

If you don't add a T fitting, you may have to deal with teh dummy light in the dash lighting up, but that would be all.

 

Are you sure you want a mechanical oil gauge? Why don't you pick up a cheap electronic gauge? Having an oil line running into the passenger compartment is just asking for trouble in my opinion. I'd prefer not to have to deal with the mess if that thing ever springs a leak.

Here you go, electronic oil pressure gauge, under $50. They make good stuff, I had the boost and oil pressure in my old Subaru. http://prosportgauges.com/