Any decent monitor you buy like Trimetric, Victron, etc. will have the full instructions and use manual included with the device. I have a Victron and it came with the pair of small wires needed and the shunt. The shunt will need to be installed between your trailer's main 12V frame ground and the frame. Some users just attach the shunt to the negative terminal of the battery and the frame ground connection. This works for most folks. The small, included, wire pair is then led back from that shunt location to the monitor panel.