It's for my 1973 Honda CL350 - not a car, but I think the process would be similar for about any gauge. The gauge bodies were nasty, the faces are faded and the paint/ink has cracked.
First task was getting the gauges off of the fork and separating the gauge bodies. A single bolt holds each body to the fork. Undo the tach/speedo cables and on to the next step. The bodies are made of up a lower chrome section bolted to the main body - 2 acorn nuts. Separate those and you can unplug the instrument lights. The speedo comes free of the lower section/wiring. The tach wiring goes inside the unit.
Next the main body has a chrome strip at the base of the black part of the housing. This is a crimped on connection. With a sharp, flat screwdriver you can open up the crimp - freeing up a lower housing that holds the instrument guts and the outer shell. On the speedo/trip odometer there is a very small screw holding the knob on. Remove the knob and separate the shell from the unit.
To get the face off, you need to remove the needle. Luckily there is a perfect tool for this - a pair of spoons gives just the right reach and even pressure to pop the needle off. Two screws hold the face on.
At the time I didn't realize the outer shell is a separate piece from the inner shell - so I taped up the faces and cleaned/painted.
First round of paint was supposed to be a flat - turned out glossy - so I re-shot with a satin black. 
Next up was dealing with the gauge faces. You can buy decals on fleabay - but that wouldn't be a true diy approach. So I fired up the photoshop. After much frustration at trying to place the indicators by mathematical approaches I realized the speed and tach tick marks are on some variable scale that was beyond me. So I broke out a protractor to take the measurements and get the tick marks in the right spots. Color matching was a best guess.
...and time to print
Since my printer has 36" paper loaded, I printed a few spares. The negative was having to hand cut the faces out with a razor knife.
Time to put the new faces on. First I popped out the colored lenses on the tach and broke out the spray glue (strong stuff).
Fresh faces...
And a little epoxy for the lenses.
A touch of red for the needles.
Re-assemble the housings - assembly is the reverse... 
and back home.
Naturally re-assembling I scratched the housing paint. No pics, but I did a touch up and all is well. Not quite factory fresh, but it's a lot better looking than it was.
