There may be an explanation to the running lights lighting due to an electrical malfunction, but another possibility should also be considered.
You did not mention if you acquired your fifth wheel new or used. If you got it new, then it's likely solely a malfunction. However if it was used, the previous owner could have inserted a switch to light the running lights when the coach is parked. This practice seems to be popular is some locales.
My first thought was, if your coach was owned by someone else you may have inadvertently tripped that switch.
Failing that, I would check the wiring harness that connects the fifth wheel to your tow vehicle for a possible connection being made that would cause the lights to go on.
Electrical troubleshooting is done by working backwards in a circuit from the lights to the plug to the tow vehicle, and testing all the way, isolating circuits until the closed circuit is found.
Do you have a multitester for your troubleshooting? not just a voltage tester, but a multitester to also test continuity?
