Select button is always on

The select button is almost always pressed and will sometimes flicker slightly or even stay off for a few seconds until i press it or the start button.

I have taken the controller apart and cleaned the connectors with iso. Even when the PCB is completely off (with ribbon cable still attached, of course) and cleaned the button will stay on and sometimes flicker on/off or stay off until pressed as mentioned above. I have tried carefully wiggling the cable slightly to see if it does anything which it sometimes does but not most of the time. Could this be a faulty wire or soldering job?

Any ideas?