First off, you'll need a multimeter, they can cost as little as $10 at Home Depot, but get as good as you are willing to spend, they really come in handy. I suggest getting one with a continuity tester that has an audible tone. That will come in handy at a later date.
Next unhook your battery and see if any of the DC lights work while plugged into shore power. If they do,then the Univolt is working. If they are dim then check them with the Multimeter. If they don't come on at all, then your univolt is not providing juice.
If you are getting lights, check a DC outlet in your coach, you should be getting around 13.6-13.8 voltsDC. However, this isn't the most accurate way of telling if it works or not. There could a be a weak output and your multimeter would show it ok. Just suffice to say if the numbers are off, or you don't get lights, then it's not working. Otherwise, here's a some thoughts:
a)Check to see that that voltage gets to the battery cables. Check it without the battery hooked up. Maybe there is a disconnect between the univolt and the battery, keeping it from getting charged.
b)You may have a blown fuse inline to the battery or in the Univolt. Check your users manual or ask here for specifics for your coach and univolt.
If the Uni is gone, you have reliably three choices that are popular here: Intellipower, WFCO(available from forum member at bestconverter.com) and the one I got and love: Iota(I got mine at www.solarseller.com)
. I think there's probably about no difference in any of these, you can get automatic 3-stage charging, they're small, lightweight and have an automated cooling fan. Installation is straightforward and non complicated. For you it's probably just an exchange of wires.
Good luck and let's us know what happens!