Looks like possible pinched wiring in tail/running lights...

[ramyankee]

I can replace the fuse and lights are fine. It is when it hits the road surface and gets bumpy, even a little. That is when the fuse blows.. The 7 point connections have been replaced.

To access the wiring I am guessing it might be in the flexible channel and will be in the lower section on each side of the fifth wheel. The vapor barrier under the unit will have to be cut out so I can have access. What I am worried about is the upper running lights that are not accessible.

Question: what do I use to repair the vapor barrier? A gorilla tape???

Any way to trace this issue to find the possible short while the unit is stationary. Would any type of anomaly show up with an ohmmeter? I

Not looking forward to this...

Thanks

[enblethen]

Cougars have fiberglass walls that require two wires to lights.

[Ozlander]

On most clearance lights, they need to be grounded to the skin to complete the circuit.

[opnspaces]

To further what enblethen suggested; if your lights have removable covers remove all the bulbs from all the lights. Then turn on the truck lights and replace the bulbs one by one until the fuse blows.

I think you're referring to butyl tape. Personally I would just caulk the top and sides of any removed lights and leave the bottom open for drainage

[enblethen]

Your clearance and running lights enter through the umbilical normally on the brown wire. In the box, you maybe able to separate the clearance lights from tailights to isolate where the problem is.
By chance had you replaced a tailight/brake light bulb? Make sure it is the proper lamp if you have! I have seen 1141 bulbs stuck in sockets for 1157 dual filament lamp.

[wnjj]

Rather than pulling the fixtures off, see what you can by just pulling lenses, unless you have sealed LEDs.

[ramyankee]

I have checked tightness on the umbilical wiring. One was probably not as tight as it should have been... That will be my first chore, remove all wire nuts and redo...

If I were to remove a fixture I guess I could use some of the tape (cannot think of the name) that you use on rv's.....

Thanks, gives me stuff to look for..

[opnspaces]

Did you replace the ends of the umbilical in an effort to resolve this issue, or is it something new?

Does the fuse blow if you wiggle, pull twist, push or bend the umbilical?

You might try replacing the fuse and then climb up with a ladder and smack your open palm against the side around each light. If the fuse blows gently pull that light fixture off and inspect for a wiring issue. If no issues found then with the fixture hanging go replace the fuse. Then go up the ladder and move the wires around to see if you can determine which wire is shorting.

If this issue is post cord end replacement you're going to have to open the ends up and find the short.

[wnjj]

I would start first by inspecting every clearance and tail light fixture. It's more likely that one of them is broken or has a pinched wire than the wiring harness itself. It's also easier to do than following wire under the frame and/or inside walls.

That said, anything is possible. My sister's trailer had the main heavy-gauge battery wire pinched between the 2x4 baseplate of the wall and the top of the frame. It was that way for years until it finally wore through the jacketing.

[enblethen]

Look in the area where the umbilical cord enters the rig. There could/should be a junction box. You maybe able to isolate which run the problem is in.
It could also tell you that the clamp on the umbilical cord could have cut into it.

[DFord]

Nothing says you need to follow the same path the original wire did. Is there an easier route to get around the problem wire?