Review on 🚘 Upgrade Your Car's Monitoring System with HOTSYSTEM Electronic Voltmeter - Blue LED Digital Volt Gauge Meter, 2inches 52mm by Josh Sharp

I assume there are two versions of this voltmeter. One has two wires and the other comes with a three wire harness. I have a 3 wire device. I bought it to replace the sand rail ammeter. At first it didn't work at all. In preparation for testing on an electronic desktop, I noticed that the connector housing on the unit was not set far enough for the pins to protrude to make contact with the harness connector. This was corrected by applying gentle but firm pressure to the case (on the unit) so that the pins were extended far enough to make contact with the harness connector. The instructions state that the connections should be: +12 V DC battery. Maybe this works well with a two wire block. However, this device is a three-wire device: red, black, and green wires. The correct wiring for this is red to +12 VDC ignition and black to ground. When connected, the green wire is supplied with +12 VDC. Therefore, it must be isolated and bonded to ensure there is no ground contact. My tests show a discrepancy of 170 mV between the VOM and the digital reading. That's enough for my needs. I gave it 4 stars because of the cable clutter.