I am not sure what chassis came under the 05 Nav, but the coach is big enough that it may be an S-Series. My Patriot Thunder is built on an S-Series and it has TWO HWH boxes - one for the slides and one for levelling. The one for slides is on the firewall behind the passenger headlight.
The one for levelling is in one of the middle bays, on the ceiling of the bay, and a few feet in from the driver's side.
I had a similar problem, crawled in and pulled all the connections off the box one at a time looking for a bad one. When I put them all back it worked fine.
There is also a bubble for setting the level, but you problem doesn't sound like that is the issue.
Good luck. BTW HWH are very helpful.
2006 Patriot Thunder