Volt Meter LED Warning How To?

Hello! New here, first post, probably wrong place but this looked like inactive area of the forum, mods., please feel free to move as appropriate. But here it is... Automobile application, wiring in a new voltmeter - VDO Viewline Onyx, to replace my old VDO cookpit. The new one has an LED warning bulb, but it is just +12V and ground - nothing in the gauge tells the LED to come on in the case of low voltage, so a "sensor" of sorts needs to be wired into the LED + and -. My initial thought was to use a 5 pin relay in which the LED +12 is on the NC contact wired to the ignition switch, so when the key is "on", that circuit is energized and the LED is lit. Once the car is running and generating enough voltage, I wanted that wire to activate the relay, which would disable the NC and kill the LED light Then, if the car started to have a failure in the charging circuit, the relay would de-energize and the LED would come back on. The trick is what component to add to the 86 terminal of the relay that would allow current to flow say when the voltage was greater than 12.5 - 13V? I thought maybe a diode or transistor of some sort, but I really don't know enough about components to make this work. Unfortunately, factory offers NOTHING for this, and their response is "well, most people just don't use it...." (O.k., then WHY did you put it in there?) -I'd like to use it... My approach may be totally wrong here, so just looking for advice on a new approach, or how to make mine work if it seems reasonable. Thanks much!

maybe use this? low voltage alarmGary Sather

Warning indicator is integrated into the gauge! It has 4-wires positive and ground for sensing and positive and ground for backlit (illumination).