This little project took me about two hours, cost $17, and retains the stock rear view mirror (RVM). This is done on the early RVM, the one that is attached to the windshield header, not the windshield itself.
I used a 3/16" drill bit, drill, 2 6mm LED light bolts, an M6x1.0 tap, some stiff wire to fish leads, heat shrink wire shielding, a little solder, and some electrical tape.
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I used Oznium LED bolts ( http://www.oznium.com/led-bolt ). I erred on the side of caution and went with the small 6mm LEDs. It provides enough light for my purpose, but I can see where the larger 11mm units may work. You could also use the LED strips and glue them along the bottom of your mirror, so use your imagination and estimate what will work best for your application. My 2 LEDs cost $17 shipped.
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Begin by removing the RVM from your car. There are a couple ways to do it, I went with the gentle method. Some say you can grab this style and yank it towards yourself and it will release. It's a break-away design, but I chose to remove the cover on the base at the windshield header and unscrewed it.
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Here is the diameter of the LED threads in inches. They come with two knurled retaining nuts. I removed one of these to have somethig to grip while screwing them into the RVM housing. It *may be possible to not use them at all and have the LEDs flush to the housing. I accidentally ordered silver bolts, but intended to purchase black ones. I rushed a little buying these online. No big deal.
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I used a 3/16" drill and marked this spot about 2" from the side of the mirror. I drilled this hole on the bottom of the RVM shell.
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Repeat on the other side. Then use the M6x1.0 tap and tread the holes. Try to begin perpendicular to the surface so the LEDs set flush. The plastic is soft, so use care.
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Drill a 3/16" hole on the top. About a 1/2" from the ball socket the mirror pivots on. This is where the wires will come out. Drill a symmetrical hole on the other side of the ball joint. Use the stiff wire and feed it through the top hole to it's corresponding bottom hole. I used about an 8-10" piece of wire. This is the slowest part and may take a few tries. Be patient and do this in a brightly lit room so you can see the wire in the housing. This took me about 30 minutes to do both.
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When the wire is through, take a small piece of electrical tape to secure the LED wires to the fish wire coming out the bottom of the RVM housing. The smallest profile you can make, the better. Gently pull the fish wire through the hole out the top and pull the rest of the LED leads through. You can now simply screw the LED into your tapped hole, then repeat on the other side.
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