connect your laptop to the tvs - and go into program/utility - at the "$" sign type "PUTD" - this will put the screen into a diagnostic mode.
while watching the screen, call in and leave a test messege for a mailbox. after you hang up, the screen should show if the tvs tries to light the msg lite. (MWL on extxxx)- if it says that it tried to light the lite then yor tvs settings are correct and the problem might be with the td1232. (try reseting dpits - prog 117)
if the screen does not show that it tried to light up the light then try deleting the mailbox and re-assigning it. as long as "extension of owner" is set correctly the light should work - if it still does not work check "others/msg waiting notification" - also check cos settings make sure that "msg waiting notificaion" is enabled.
you can also try resseting "DPITS" in the tvs by going into hardware settings and change the system type to an analog and then back to td1232.

**remember to go back to the utility command and at the "$" sign type "PUTD" again to turn off the diagnostic mode.