i think your  assuming  wrong.   the power  goes  through the  tip    to the  center  sleeve  as  ground     on a trs  cable   since  your  putting   a mono cable  in  your   creating  a  circut  that wasnt   originally there   your  attatched  to    the  ground  terminal  and  at the same time  the   terminal  that the   sound  circut  connects  to.  so  technichly  your  creating  a short  with the  mono cable  and  thats  probably  why  the  red  light  goes  off. is it gonna   damage  your  guitar.   most likely not  but ill bet  your  sending current  to  the  guitar through  the  pots  and   pickups.    heres  how to find  out .   hook up a  meter   to the  mono cable  that  plugs into the  guitar   tip  to shank. if your getting  power  there    well then you have  completed  a circut.   since  the  ab  box   is designed  to do this  . well  is it  working   correctly.  if not it  may be shorting  internally and  who  knows  what that will do over time.  since  these  switches  arent  readily avalable...  do you  want to take that chance  is the  question.  you might  fry a resistor  over  time.   i dont  see these  avalable  anywhere.

as to the   amp end  it  wasnt  designed  to sent  power to the  amp as  far as i know  . so that end  should be fine.  if you feel you need  to do this  with     this ab switch  with  another  guitar that does  not require  power   id  say  stick with the  stereo cable.  in most cases   the contact  in the  guitar  if you have  a good output  plug  is  low  on the  shank   and  the  tip. the trs   should  work fine. ive  used them this  whay  when i diidnt   have  anything  else  with  no problems.

my advice  to you  would be  to  not use this  switch  in that way. go buy  one  or build  one.  just curious  what are  you trying  to acomplish   with  that rig.