I have a 2003 wanderer, and I just noticed that my running lights are out on it. The brakes and turn signal lights work. I was wondering if it was a fuse, and if so where would i locate the fuse on the trailer.
The running lights should go on with your tail lights. You didn't mention if your tail lights work. If your taillights work and the running lights don't, it may be a bad connection somewhere or a fuse. I don't know where the fuse would be located if it exists. Also check for burned out bulbs.
There usually is no fuse on the trailer - just wiring to the lights themselves. The power is supplied from the tow vehicle and that's where any fuses are - on the tow vehicle. As Jake says, they are wired to the tail light circuit because they should be on whenever the tail lights are on. It's not unusual for most or all of the marker lights to be out because the sockets have become corroded - the lights are often pretty cheap and they commonly leak after awhile, exposed as they are to driven rain and dust. But it could be simply a disconneted wire or corroded splice joint.
We just bought an old trailer. Every marker light was out and I wondered if there was some wiring issue or a fuse, but knew that they are supposed to be on when the tail lights are on. We saw that one of them does come on and started testing them all with a new bulb. All but that one are corroded or the bulbs are shot from condensation. A little WD40 and 12 new bulbs will fix it for us.