Out side marker lights.

Something is mis-wired. Get it checked out.

That would be annoying at a campground.

The positive wire to those lights (brown in 7-pin ISTR) must be touching a 12v powered wire but is missing the negative path to make it a circuit.
(If shore power that makes the converter go on makes the converter the 12v source, then the lights would be on just from the battery and no shore power too.)

So it must be the 120v ground prong on the shore power that completes the 12v circuit because the Rv frame shares its negative/ground with both 120v and 12v. You could test for that by using a 120v plug with no ground prong (via adapter) --not sure that is right, but as far as I got until the next thought comes along!

First suspect is the 7-pin trailer end plug if strands of wire on the brown wire pin screw terminal are loose and touching over to pin 4's also loose wire strands that might be sticking out.

Then perhaps farther in where the 7-pin cord wires meet the trailer's wires. On our old 5er that was in a fuse panel under by the kingpin, but some 5ers have that farther in under the bed I have read on here. Loose strands touching or else cuts in the wire insulation allowing bare wires to touch.

jdc1 wrote:
That would be annoying at a campground.

Yes it would but, I've seen several people who wire their rigs so the marker lights stay on all the time while on shore power.
I think it's rude while in a CG but, the 'all about me' attitude kicks in and people do what they want to do. Just like loud music, barking dogs, etc..

Exactly which lights are lit? Tail lights, or the marker lights at the top?

When NOT plugged into shore power, the lights are OFF? Do you have a Rear View Camera on this unit? Doug

gbopp wrote:

jdc1 wrote:
That would be annoying at a campground.

Yes it would but, I've seen several people who wire their rigs so the marker lights stay on all the time while on shore power.
I think it's rude while in a CG but, the 'all about me' attitude kicks in and people do what they want to do. Just like loud music, barking dogs, etc..

The really cool folks are those who wire in a hazard flasher so the running lights blink on and off all night long. That always leaves me impressed.