If incandescent, as posted above. it doesn't matter. Neither positive or negative will be in contact with the housing in a marine nav light, most of which have plastic housings anyway. An incandescent bulb is a glow from the resistance of a filament and it matters not which lead is at which end of it. On an LED light, positive has to be connected properly.
Interestingly, most marine interior dome lights switch negative if you go by color coding - black through the switch and white or red direct to the bulb. I usually reverse these when I install them.
04-30-2011 10:39 PM
It probably doesn't matter in a simple dc circuit like this. But it is probably a good idea to find out.
04-30-2011 10:37 PM
Assuming that the bulb is an incandescent type (regular bulb with a filiment), there's no positive or negative. You can hook it up either way.
If you want to be sure, use a multimeter to be sure that neither of the two black wires is connected to the light housing or mount. Most likely they're not, so you can hook it up either way and it will be fine.
04-30-2011 10:13 PM
I am sure this is a simple question so I accept that fact it and I may sound a little dumb asking but here is my question:
I bought a new Perko stern light. When I opened it up I found two black wires. I saw nothing to indicate which is pos or neg. The wires in the boat and on the old stern light are what I expected in the new light red and black. Hearing all the horror stories about faulty wiring damage I do not want to hook it up with out checking, is there some clue indicator that I am missing on the black wires or does it really not matter which is pos or neg when hooking up a stern light?