Measuring the Workspace
First off you need to decide where you are going to put the on-off switch for the light. I decided to put it in a 5 14" bat cover that will be getting a bay bus installed in it at a later date. The switch is round as you can see and requires about a 34" hole. You need to draw a line across the center of the bay cover.
Draw a couple of pencil marks on the edges of the cutout template that align with the centering lines on it and pull the paper off the back and stick it to the bay cover. Then proceed to drill or cut out the hole with a utility knife. A 34" drill bit should work just fine but the biggest but I had was 916's, so I proceeded to drill a 916's hole and enlarge it using my Dremel tool.