I understand that you are using MCI and that when you call a station, it will call forward to the correct greeting and that only the message waiting light is not working.
Was it every working? Is this a new install?
a. Try another port or another mci card. I have had ports go and recetly, I had a card die.
b. If you never had this working check
F87>087:MCI Interface :A (should be an A)
F87>043:VMS Indication:USA:A (should be an A)
There is an MCI tool that will simulate what the phone system is supposed to do. Ask you local NEC authorized dealer to follow this link and download it for you:
Then you can bypass the voicemail and try to turn on the light directly to the mci card.
c. Check: CM08>443>0 (VMS with MCI)
CM08>444>0 (message waiting lamp control from MCI)and check 1225>vms station> 3 for mci and 0 for dtmf integration.
d. Are you using the correct cable? Use a RS-RVS-4S CA-C / RS RVS-15S CA-A cable or RS NORM-4S CA-A.
e. For the Port 1 and Port 3, data speed 9600 bps cannot be set.
f. Check SW0. There are 8 dip switches. Check them against your manual.
Keep us posted.