Posted by John528 on the E39 Message board.
1. The first thing you do is disconnect all power to the lights.
2. Then, look down on the assembly from above and remove all four screws (bolts, really) holding the assmebly in (two are on top and two are behind (down low)). Mark the spots with a magic marker before taking the bolts out so you can realingn them when you are done.
3. Once the bolts are removed, you can slide the entire light assembly out. Be careful of the outside corner, as it is sort of clipped into the body.
4. Replace your existing corner bulbs with amber bulbs. I went to Pep Boys and showed them my existing clear dual filament bulb and they found it for me. The code for the proper Sylvania bulb was 3357NALL. It cost all of US$8.50 for 2.
4. Once the light assembly is out, carefully remove the body-colored peice of molding that is attached to the bottom. It just sort of pops off if you use a flat head screwdriver.
5. Then, begin loosening the clips which hold the lights and the plastic lenses together. There are a lot of clips, so just release them one at a time using a screwdriver. Ignore the spot welds in the plastic -- just break thru them easily.
6. When you pull the lights apart, you are ready to take the old backs and attach them to your new fronts. Because you got new glass lenses, you do not need your old ones. Pop the pieces together and make all the clips to go back together.
7. Repeat in inverse order steps 1-3. Be sure to attach the power for the corner lights (your new amber ones before you get the assmeblies stuck in place -- it's hard to reach back there otherwise.