Advice on installing a voltmeter

[fixkick]

3rd wire would be the decimal point? , back light, or range setting, or mode , or gain. RTM
the LED 7 seg.display's come in near infinite form (this is voltmeter)
the data sheet for these answers that question, 100s of brands.
what this is , is a dedicated, digital volt meter. (uses a display and a analog to digital converter inside) just like A DMM but with no ranging.