fixing an electrical short

[David]

As usual, what I think will be a fifteen minute job becomes much more! While replacing a 12V light fixture on my 85 Cat 30, I turned off the AC power but not the DC. Thus, I seem to have managed to short out a part of the system. Whenever I turn the cabin light switch on, I blow the fuse. The port lights work up to the head, but then darkness on the starboard side and V-berth. Any suggestions on trouble-shooting and repairing this electrical problem?

 

[Hugh]

reverse wires?

The only thing that comes to mind is that your lighting fixture has a ground fault or is mounted to a ground source, and powering on the cabin lights causes a short to this ground. Check the wiring to the new light, and make sure it has no exposed areas that may be touching metal (or each other). If the fixture itself is metal, see if it is screwed into/making contact with other metal. If so, you might try switching the + and - leads at the fixture.The best way to troubleshoot is to 1) take off new fixture and wires, tape off ends, and try cabin lights. No problem? Good, its your new fixture or the way you hooked it up. Try reconnecting. Still good? Mount it. Still good? You're done.Good luck. (Bring plenty of fuses...)