If you are blowing a fuse and have replaced it once and blows again you will have to systematically go through the circuit to check for shorts or a bad fixture. Work your way from the power source to the end of the line/cirucit checking each component. Shorts in MH wiring can be time consuming to find, so if you can troubleshoot on your own it could save you some $$ in the end. Fuses do fail over time, so it could just be a worn out fuse.
If your are blowing the fuse whenever it is replaced I would suspect that a wire (Posistive/Hot) has become chaffed by some object in the wire run over the years and is coming in contact with the motorhome gorund, or you have a bad fixture. I would drop each fixture to check as much of the wiring as I could see to make sure the wire insulation is sound. Disconnect each fixture and power up the circuit, if the fuse continues to blow that would tell me it is somewhere in the wire run, if it doesn't blow a fixture is shorted somewhere internally. Hook up each fixture until you find the bad one. If each fixture has it own switch be aware the switch could be the culprit, that's why the only real way to be sure is break the electrical connections prior to the fixture.
Hope this helps
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