I took a look to make sure the cords were in the correct slots, which they are.
When the new phone was plugged in her ext did stay, meaning I didn't have to program the ext to the phone.
I am using the M7324 series. There is no slide switch on amp box because there is not an amp box.
The headset is in working condition.
I have tried all suggestions, please let me know if there is anything else I can try.