Re: Nav lights on causing buzzing noise under cowling
You obviously have some wiring issues. You also have two electrical systems on the boat. 1) the harness that runs from the engine to the control box at the helm carries power to the ignition switch (among other things) and from there it feeds power to the gauges. 2) The other accessories such as your nav lights are not powered from the engine harness but rather from the "boat" harness which is the smaller (#6 or #8) pair of wires connected to the battery. That circuit runs forward to power the switches and other accessories including the NAV lights. Have you actually removed the engine cover as suggested to view AND hear where the noise is coming from. You more than likely have a ground problem because when electrical things begin behaving in a weird fashion it is almost always a ground issue. If all gauges had quit, then there is generally a loss of power or ground at the first gauge in the string since they are typically daisy chained from one to the next. If you lose just one or two gauges it is generally a wiring issue on that/those gauges. Since the internal gauge lights are wired to the NAV switch that powers the nav lights, you have an interaction between the engine harness and boat harness and that probably means a grounding issue. Current will seek out an alternate path to get back to the battery via any means when the normal ground paths are interrupted which accounts for weird electrical events.
