There are many possible reasons for this sort of fault. e.g fuse blown on one circuit, broken wire, corrosion, circuit removed by a previous owner. Because of this, members of the forum will have great difficulty in trouble-shooting your electrical system. The best solution is to use a digital voltmeter and folllow the circuits from the distribution board until you find the fault. Assuming you haven't already done so, the purchase of a meter (perhaps $30), discussed at http://www.airforums.com/forum...voltmeter+nick
and studying a book on 12 volt
electrics (search the forum for "Harold Barre", one of the relevant authors), will give you immense satisfaction in tracing faults, and set you free from having to employ persons of unknown ability to solve future problems. If you already have a meter, and know how to use it, I apologize for "teaching my grandpa/grandma to suck eggs." Good luck.