I converted my rear lights over to LEDs by using a pair of trailer lights I found a Pep Boys. They were $25 per light, and come in a bucket. The LED light is retained in the bucket by using a snap ring, which is easily removed.
To install these into my stock lights, I used a heat gun on 'low' to heat the stock housing. The lens is retained into the housing by a couple tabs around the light. I used the heat around to tabs and gently persuaded the housing to 'let go' of the lens. It will pop out after the tabs are separated from the lens. I chose this route due to the age of the plastic and trying to pry/force the lens out would probably be destructive.
Once the lens is off, I took the LED out of it's housing. Using a cut off wheel I cut the bucket that the LED came, in down to where it fit into the stock housing. The way mine are installed is the LED and bucket just barely clear the lens once it is installed again. Once the bucket was cut, i cut four slits into the bucket, making 'tabs. I bent the tabs so they hugged the contour of the stock housing, using two small self tapping screws I retained the bucket into the housing with those. From the 'outside' in, so only the hex head shows from the self-tapping screw.
Once the bucket is installed, a hole can be drilled straight through the back to allow the wiring to pass through the stock hole in the housing. The LED will then be installed and retained using the supplied snap ring. The lens will be reinstalled onto the housing and using the same heat gun trick, the tabs are 'closed' again. Retaining the lens. Use care when doing so, don't mess with it too much, you may end up breaking the tab off the housing!
The wiring is very straight forward, it is power and ground. You can either cut the stock connector off the wiring harness and splice it, or find a source for empty 1157 bulb sockets. I initially went with empty sockets due to me having a relatively new rear wiring harness. The wires go through the empty socket and are just soldered on the ends, they then go into the stock bulb connector. I did this due to the new harness, as well as planning on upgrading to a full aftermarket harness in the near future.
You may have an issue with your flashers under the dash. The old thermal flasher I had would not properly blink the new LEDs. I went to the parts store and purchased two electronic flashers in which worked out for me just fine. I have heard of some having not all electronic flashers work for them, so it may be trial and error. The number on my known good flasher is "FL-32" ($9ea at Checker, you need two)
http://shop.oreillyauto.com/ProductDetail.aspx?MfrCode=BLZ&MfrPartNumber=FL32&PartType=121&PTSet=ALEDs
Stock housing with lens removed
Bench testing
Stock bulb pattern
new LED, MUCH brighter!
