Here is another view of what was shown already above...
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I have done this on a few ocassions to light up around the trailer. It will run your trailer battery down if you leave on for a long time if you are not connected to shore power.
There is a company that sells a RVGLOW plug-in to your 7-way trailer plug that does the same thing...
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You can also very easily plug in a standard ATC type automotive type fuse in this connection plug. I would use a 15AMP fuse I guess... Each of those automotive incandescent bulbs will probably draw at least 1AMP each.
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Some folks have wired in a permanent wiring from the 7-way trailer cable junction box to a wall switch inside the trailer door to turn these running lights on. This is a great feature to have when emergency services folks have been called to come to your trailer and would help in identifying which trailer to come to to.
I suspect you get some nasty comments from other neighbor campers if all of your trailer running light are flashing all night...
Please be neighborly...
Roy Ken