trailer dual filaments reversed symptom

[Filbert]

'06 CC: truck's lights all okay.
trailer lights seem to have filament reversed, as in
running light is bright and brake/turn is dim.
both sides.
symptoms are the same on trailer and new magnetic spare set.
the 2 fuses under the hood are good.
do not see any fuses under the dash.

how to check the relays?

[Forestteck]

Maybe a ground wire problem on the trailer. Also check to see that you have a good clean hith ball/trailer hitch(ground travels through hitch). my 2 cents.

[Filbert]

I find that the ground lead on the 7-lead socket has no continuity with the frame or tow hitch. I assume there should be.
Is there a fuse for the ground lead?
Any reason not to simply directly ground that lead locally, perhaps with a fusible link, rather than hunting for the break?

[challenger3x2]

Maybe wires on truck end of 7 pin connector have worked loose. Also there are at least 3 fuses plus a couple of relays under hood that are tow package related.

What type of trailer?

Do trailer lights work properly with other tow vehicles?

[Filbert]

Apparently a false alarm.
The system works perfectly on third and fourth trailer tried.
Thanks for the suggestions.