2003-04 Cadillac CTS Upper Grille Installation Instructions

Step 1: Remove factory grille shell. First, remove the four plastic screws located on top of the shell (two in the front & two on top). Then remove the four plastic screws located on the bottom (directly behind the grille shell). The bottom screws are much harder to remove as you have limited access to them. You can snap them out which will render them useless for future use, or you can take your time and slowly work (shimmy) them out using a flat head screwdriver.
Note: If you intend to install the grille shell back on to the vehicle you will need the plastic screws to do so. If they are broken when removing the factory shell you will need to purchase new plastic screws from the dealership.
Step 2: Tape over the grille opening to protect finish (see figure 1 & 2). Next, using the necessary cutting tool (die grinder, air/pneumatic saw, jigsaw) carefully cut the plastic guides from the grille (see figures 2, 3 & 4). Do not cut into the exposed portion of the front end.
Step3: Now file down rough spots until smooth (see figures 5 & 6). Once finished you will have a nice smooth surface, which will allow the billet grille to rest unobstructed in the freshly trimmed opening (see figure 7).
Step 4: Fit the grille insert into the trimmed opening, attach the two extension brackets to the top two brackets (left & right) using the 10-24 x 1” cap screws and k-lock nuts provided, then attach the two bottom extension brackets using the 10-24 x 1” cap screws and k-lock nuts. Before tightening be sure that you have the proper distance needed for a precise fit.

source