Mysterious electrical box behind main panel

[jakell]

I have a 1988 C34 and have been doing some electrical work on the main electrical panel and found an interesting item.  I don't have a picture of it, but will get one next time I am on the boat.  It has 4 wires running to it, 2 inputs and 2 outputs, and is approximately 4" x 4" x 2" and is mounted behind the panel.  The positive "red" wire from the cabin lighting switch runs to the input of this box.  The positive output of the box feeds only the cabin lights.  The ground feed for the cabin light circuit also runs through the box, the negative bus bar connection runs into the box.  The ground wire that feeds the cabin lights is connected to the negative output of the box.  The lighting on the boat is completely original with no apparent modifications.  Any ideas what the box is, I thought it might be some type of isolator, but why would that be on the cabin lights?  Any ideas welcome.

[Craig Illman]

I'll make a wild guess, but possibly some sort of filter to minimize electrical noise from florescent fixtures that might affect the VHF?

Craig

[jakell]

Thanks for the reply, that is an excellent idea.  It definitely makes sense.

[Stu Jackson]

It would help to know what, if anything, is inside the box.  The PO could simply have made it a sub-distribution box for the lighting circuit(s).

[jakell]

Here is a little more description.  It is a solid block of what looks like cured rigid epoxy and it has a metal bracket connected to one side, that is why the filter idea made a lot of sense.  It only has two wires in and two wires out.  It has no markings on it.

[Jon Schneider]

Is it ticking?   

[Ron Hill]

jak : Did you ask the previous owner what that "Black Box" was installed for?   

[Tom Lanzilli]

So this is not really an electrical box it seems more like a solid state device.