We have a IDCS 500 I set to key 24 the VMMMSG which works when we hit it to go to VM. My question is how do we get that key to light (lamp) up or blink when we have a message I know it works on the 100 model. BTW we have a cadence VM.

Make sure there is an extension assigned in that mailbox. That is what tells the cadence which lamp to light.

there is one but still nothing whatelse

Sounds dumb, but try unplugging/count 10/plugging in the phone. If that doesn't work try deleting and adding back the VMMSG button.

After that you might try deleting and adding back the mailbox in Cadence (try it on an unused extension/box first, if you have one).

Is this the iDCS 500 with 4-digit extension numbers? Or did you reset that to 3 digits? If the former then that may be the issue, I've never tried to use differing switch/VM extension/box numbering plans in the same system (nor have I run a Cadence in a 500, but the manual says it will work, with message waiting lamp).

If your set for 3 digits on both, then try an msg key and see what happens. If still no light check your vm/aa options, assign mailbox and vm in and out.Then your station groups

If still no go I think it might be best to get a tech onsite.

Try this go to a phone and manually dial 41 and a
ext number. See if light is on. To clear dial 42 and ext number. This will test if the phone is ok or
vm is not sending proper code.

Also check in Vmail ring group is set up right.