Trailer light/fuse issue

I had a blown fuse for the trailer running lights circuit so I replaced and it and made a run to Mille Lacs during daylight. All Good. On the way home (night time) lost running lights just south of Zimmerman, blown fuse. I had a side marker light out so I replaced it along with the other side markers, replaced fuse and all was good. Made a few short trips with running lights on, all good.
Now I make another run to Mille and I lose my running lights coming home just south of Zimmerman, almost exactly where I lost them last time! Left from same landing and ran about same speed home so it seems more than coincidence.

Any ideas? I’m stumped.

How old is the wiring in your trailer? My guess is that you have a spot where the insulation is worn through so the bare wire occasionally touches the trailer frame. That will blow the fuse. There’s a good chance you’re going to have to pull some new wire.

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How old is the wiring in your trailer? My guess is that you have a spot where the insulation is worn through so the bare wire occasionally touches the trailer frame. That will blow the fuse. There’s a good chance you’re going to have to pull some new wire.

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Exactly what Rootski said.

You’ve got a short somewhere in your wiring harness. It takes the longer trip to make it rattle around enough to eventually touch metal and ground out, thus blowing the fuse.

You can certainly try to find an obvious wire chafe and fix it. This can be time consuming and frustrating, so the fast/easy fix is to replace the whole harness.

If you replace the harness, make absolutely sure that the new harness is protected everwhere it passes through the frame. ANY metal edge that the wire touches will eventually wear through the wire jacket and cause a short. Use rubber grommets to protect any hole that wire passes through.

Grouse

im an electrical engineer, and what thes guys said makes a lot of sense. im concerned though we are missing the big picture.zimmerman may have a electrical expanding and collapsing field which in turn causes your wireing to reverse polarity creating an electrical void between the elements in the bulbs….i would stear clear of zimmerman, just in case…

I had a similar problem on my last boat. every once in a while the fuse would blow on the truck. Turned out that the center light bar on the back of the trailer was not sealed completely on top and would let a little water in each time I launched. The bottom was sealed fine so it wouldn’t drain out. When the water would slosh around just right, it would cover two of the LED connections and short. I drilled a hole in the bottom, drained the water out, and then sealed the entire thing with liquid electrical tape. Worked fine for a couple months until I got around to replacing the light.

Last year I had the exact same problem. I took all the old wire out and inspected it and did not see any damaged wiring. The only thing I could see is there were plug together connections in the frame of the trailer and one was partially pulled apart showing some bare contacts. Even seeing the connections partially apart it did not look like it would short out. Long story short I rewired the trailer using 3 wire extension cord, replaced the side marker lights and replaced the male plug to the trailer. Problem solved.

Thanks everyone, looks like a Saturday project soon.

Same problem here also, two years ago. Turned out to be corroded side marker lights, causing them to short out during travel. Decided to rewire the trailer, and replce all ligts with LEDs. No probems since.