Have to agree with Ian,
Was coming back from 75klm out of 1770 when we started smelling that burning insullation smell. Thought we were a bit too far out to be getting somethying from the land. We stopped the boat and isolated the batteries. This was right on twilight and I had turned the nav lights on only 10 mins ago.
Didn't take long for us to find the port LED nav light had burnt out and the fuse (10amp) was still intact . There was no reason for this to happen it just did.
You get a new lease on life when this situation is occurring i.e WTF is burning !