An alternative way of doing the joypad pause button mod,by only wiring one of the joypad's directions to an added small momentary push button that is installed in the joypad (as in the guide below),instead of two.( It just means you hold a direction and then press and release the switch).As found herehttp://www.smspower.org/Development/JoypadPauseButton
And also a way of having a reset button on your joypad ,again,using a quad NOR gate IC..
Install/attach the NOR gate IC as per the OP's method in the guide above,or just wire it up and attach some double sided tape onto the top of the quad NOR gate IC and flip it upside down and stick it down onto another of the sms's IC's.
LED's can be added with a few extra components ,if there is a need. Any mistakes,please let me know.
Note that this mod is done on an early version of the sms,from 1986/87,so can't verify it's use on later models of the console.