Review on 🚗 MICTUNING LED Digital Double Voltmeter: Round Panel Voltage Monitor Blue for Cars, Pickups, RVs, Trucks & Dual Battery Packs by Jason Franco

I see two common themes in the negative reviews 1) Primary worked Secondary didn't work The master must be connected for the secondary to work. Route the main battery cable to the main battery Route the auxiliary cable to the auxiliary battery. Wire - to common ground. It's easy to determine which terminal belongs to the main, it's at the top, just as the main is read. so that the counter is constantly lit. Route the main wire through the ignition wire in the fuse box using the wiring diagram. Or connect the on/off switch via the main cable. I haven't decided yet which way I want to go.