Painted Ocean,
This is what I found on running lights onboard u-boats. I hope this help you out.

Running Lights
 
 
        The following running lights are provided:
 
 
        1.  Port and starboard side lights.
 
 
        2.  Mast head light (portable).
 
 
        3.  High and low stern lights.
 
 
Inspections of the above running light installations reveal the following:
 
 
        1.  The side lights are provided with appropriate red and green lenses.  These units are pressure proof, the leads being led from the conning tower by means of stuffing tubes and conduit.  In general, the vertical height above the deck is approximately 3 feet higher than on late design USN submarines.  The angle of opening of the light is identical with present USN equipment.
 
 
        2.  The mast head light is a portable, sheet metal, drip-proof light which can be secured to the forward periscope when it is in a slightly raised position to provide a mounting surface.  The power supply is obtained from an outlet in the Conning Tower, the lead being run up through the Bridge Hatch. 
 
 
        3.  The High and Low Stern Light fixtures are designed as pressure proof fixtures, the leads being run from the Conning Tower through conduit and stuffing tubes.  The angle of illumination and physical size of the fixtures is approximately the same as USN fixtures.
 
 
        4.  All running lights are energized from the regulated 110 volt D.C. bus and are controlled from a common switchbox in the Conning Tower.
 
 
        5.  The stuffing tubes used with these circuits are provided with drains within the vessel.  In these drains are installed petcocks which allow the conduits to be drained to the bilge in the event the conduit leaks at any point.
 
 
        6.  It is observed that the German has not developed a pressure proof receptacle for use on the Bridge.