You need two diodes and a Double throw double pole (DPDT) switch with center
off. The switch will have 6 poles. A pair at each end and a pair in the
middle. Connect the middle pair to your DC power and ground. Connect the
end poles diagonally across from each other and run from either end pair to
the lights. I use that method to control the direction of my fuel and water
transfer pumps.

At each of the two lights add a diode in series with the direction opposite
each other as Heikki described.

With 3 wires and a double gang rotary switch you can control 6 lights.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"OldSailor" wrote in message
...

"jim.isbell" wrote

BUT, you really need only a single pole three throw switch because you
only need to switch one of the wires, the other can go to both bulbs
all the time. AND again, you dont need diodes whether you are talking
DC or AC


If the switch is located at remote point - say on the boat's electrical
panel and the light is for example a 2-bulb steaming light/deck light,
then
would your scheme not require 3 wires from the switch to the lights?

I have also seen diodes used - presumably they overcome this problem by
only
requiring 2 wires up the mast?