I know we have all seen the 4" LED write-up, I've done one previously myself. But I'm not so thrilled with that one, and my wife wanted me to install them on her '93 YJ, so I thought I would give documenting this procedure another shot. I bought these grommet mount 4" LED lights at Wal-Mart for about $15.99 each, and I bought an EL-12 electronic flasher at the local Advance Auto Parts for about $11.99, but I ended up not needing it because I replaced her flasher unit previously with a "heavy duty" model which surprisingly worked perfectly.
First I removed the four phillips head screws that attach the factory lenses to the stock housings on each rear tail light and then removed the three 10MM head bolts that attach the housings to the body. Once the housing is unbolted you can disconnect the wiring connector for the tail lights.
I measured through the oval wiring access hole up the the top of the wheel well. There is just enough room vertically to mount these lights. If you cut the hole too high, you will cut into the top of the wheel well. If you cut the hole too low the grommet for mounting the light will interfere with the trim around the gas filler.
As you can see here, the upper edge of the oval hole is 3-5/8" from the top of the wheel well. I really wanted to make sure that I didn't chop into the top of the wheel, so I used 3-1/2" as my measurement when calculating where to cut.
Next I covered the entire area with tape to help control paint chipping/damage during cutting, and to provide a place to make my mark for drilling. I measured the 2 lower bolt holes & found that they are 2" (center to center) apart from each other. I marked the center between the 2 lower holes & then drew a vertical line from that mark to the center of the upper bolt. This will guarantee that the lights are centered L & R exactly the same as the factory lights.
I measured 3-1/2" up from the top of the oval hole & made a mark on the tape to indicate the location of the top of the wheel well and then made a mark on the vertical line 2-1/2" below it. This where I centered my 4.5" hole saw, as called for in the LED light instructions. I used a center punch to make a small hole in the body to prevent my hole saw arbor from veering off course & then cut the 4.5" holes in the body. Leaving the tape in place, I used a round file to smooth the cut & remove any burrs, and then gave the cut edge a quick blast of paint to prevent rust.
I removed the tape & let the paint dry while I prepared the wiring.