I have a 2008 Winne Destination and had the same problem.
You need to find the Freightliner Aft fuse and relay box.
I found mine in the compartment with the power cord behind a panel that does not look removable. It was a real bear to get access. I made an access door in the panel before replacing the panel.
What you are looking for is a covered box with many cable plugs going to it.
It is the same as the one inside the (large) forward fuse box.
Use care removing the panel if you have 12 volt circuit breakers in the compartment. (The aft fuse box is below)
Returned after dinner>>>>>>>
I think the post below nailed it.
At least, I hope so for your sake. A lot easier than what I went through. I know people (Dealer shop) tapped into the MH lights because they could not find the fuse box.
Good luck.