sounds like you are getting a selector fault do you have a tool, if so when the light is out check for selector fault. Over the years, we have had to fix dmc cars with no tool, one thing i always tell the young guys, if a dmc is down, and you have no tool, and no idea what is going on, check the led on the selector board, if at all possible, if it is out, it is more then likely a selector fault. bad tape guides, bad switch tree contacts, or wiring are the likely suspects.