How can I tell whether a navigation light is working when I have turned it on?

The Maretron development team has found this particular device which can monitor current through a wire. This is especially usefull dermining if in fact a vessel’s light is turned on and not burned out. There are two variants of this device for AC current and DC current. The Device consists of a Hall-Effect sensor and a relay. For monitoring DC current the device will close a relay switch when the current is detected. The AC current switch will close a relay switch with current 350ma to 100A. The SIM100 will transmit PGN 127501 On/Off, when the relay Switch is closed. YOu can find the data sheets of the devices specified above in the Attachments section of this article.
For detailed information please visit the following link: 
http://www.crmagnetics.com/newprod/relaysg.asp