The module is under the dash, just above your foot on the gas pedal. It has a large gray plug (lots of wires). The code is on a tag on the passenger side of the module. You can read it upside and backwards with a mirror. It should be the largest numbers printed on the tag.
Thanks to Glen Murdock:
I just bought a 1999 SHO and was wondering if you could help me. I don't know where the keyless entry code for the door is located. On my 1992 SHO it is stamped on the inside of the trunk lid.
Thank you for your time
There is a paper tag on a silver metal box under the dash, above the gas pedal approximately.
I don't bend that way, so I took a small digital camera with flash and kept taking pictures till I got a good one of the box. Then I took it to the computer, downloaded, put it in Photoshop (or any other photo program), rotated it, enlarged and fiddled with contrast etc till I could read the numbers good enough to make a guess at the code with only about 3 possible combinations (6 looked like an 8 for example?)
Got the correct code on the second try.
Lots easier than trying to fiddle with a mirror and flashlight (tried) or to get under the dash (impossible).