I'm trying to change the code on craftsman 139.53674SRT2 keyless entry pad. The directions say to enter code & push #, then light will blink. When I do this the garage door will open, instead of lights blinking. It's like it thinks # is enter. Could there be a short?

I don't know where you are getting the instructions from, but there are two different ways of programing. One using the LEARN BUTTON and LED on the opener. It is where the low voltage wires enter the unit. Depending on the details it might be behind the light lens.

The ohter uses the multifuntion wall control, if you have that.

Note the SEQUENCE of operations. None of them follow what you describe.

http://lib.store.yahoo.net/lib/aaaremotes/976LM-manual.pdf

And this is the manual for programing the remotes.

http://lib.store.yahoo.net/lib/aaaremotes/971lm-manual.pdf