The guage must come out. Those four nuts are a little hard to get at but not impossible. I use a 1/4 inch ratchet. Once the guage is out you will see that the chrome bezel is crimped onto the guage housing in a few places. Uncrimp these and you can remove the bezel and glass.Be careful not to drop the glass. Carefully pry the needle assembly off the brass stem. You don't want to break the stem. It's very fragile. I've had to hold the guage upside down and take a toothpick to put a drop or two of penetrating oil on it. Once you get the needle assembly off you'll have to pry up the tabs on the chrome button the needle is mounted to. Now put everything back together the way you took it apart. Hold the guage upright and make sure the needle registers 0 on the dial before pressing it on tight.