The wattmeter measures the current running directly through it. That means that one side is connected to the battery and the other to the controller. When big currents run through wires, the voltage drops. The longer the wire, the more it drops, and the thicker the wire, the more it drops. The thickness of the wire is more important than the length. Therefore it's best to keep the wires as short as possible. If you want to put the meter on your handlebars, you need only to lengthen the existing wires with very thick wire like this, which works, but looks a bit horrible. You need 30 amp wire that you can get i Maplins. Bear in mind that it needs to run all the way from the handlebars and back to the controller - nearly 3 meters. I did this and there was no noticeable drop in range or power, but there is a loss of a few watts.
On some wattmeters, you can remove the bit that does the current measuring and connect it to the meter with thin wires, which is a much neater solution and wastes less power than the thick wires method. These photos show how I do it. It's slightly different for you meter. You need to check out what's inside yours. However, this mod requires good soldering skills.
