Locate the marks on the inside of the trunk lid. If the spoiler features a brake light, another hole will be required for wiring to come through. 2. Make the holes. The spoiler bolt holes should be ⅓ inch, while the hole for the wiring should be slightly wider. 3. Put a small amount of car paint matching the one on your Honda Civic spoiler in each hole and let it dry. 4. Mount a spoiler and secure it with the bolts from inside of the trunk. 5. If there’s a stoplight harness, pull it through the dedicated hole and through the panel to the brake light. Take off the negative lead on your battery, unplug the car brake light cable, and hook the spoiler wire to the terminal.