I spoke with Tiffin Service yesterday; got some advice and the problem fixed. I was into it for better than 2 hours, though. What should be a simple fix is anything but -- a design fiasco.
The access must be accomplished through the engine compartment.
First you must remove one end of the 8" vent tube -- I removed the bottom end. The tube is removed from its "home" by some (rather severe) yanking.
There are two bolts on the mid- and top- far side of the taillight assembly. The top one is easy to miss in this cramped compartment. The top bolt has barely enough room for a socket; the mid-level one needs an open end (7/16) to remove it. Mostly, because of the size of the area and the location of the bolts, this is done "blind" - by feel or touch -- as both arm and head do not fit in this space.
Finally, there is small "set screw" mid-level on the near assemble wall. It nestles behind some wiring for the taillights and is not immediately obvious.
Once the tail light assembly is free from the m/h body, there are 3 more screws in the back of the assembly to allow access to the bulbs.
Once I got to this point and grasped the offending bulb, it suddenly lighted -- apparently the result of dirty contacts. I sprayed the receptacle and bulb contacts and achieved a solid light.
Re-assembling presents its own challenges,
After replacing the 3 screws to re-assemble the taillight assembly, I tackled trying to replace the 2 bolts and set screw. Holding the assembly in place AND reading into the engine compartment simultaneously proved impossible. I enlisted the aid of my wife to hold while I attempted to "nest" the bolts into their proper location. I kept missing the threaded hole trying to feel "blind" where it should go.
The setscrew is easier - although still done "blind."
Replacing the fabric of the vent tube over the air cleaner was another time consuming chore. The fabric kept folding under itself and inside the air cleaner rim. But with time and persistence I eventually got it.
It does seem like there is a better solution to access to the tail light bulbs.
Tiffin?
Don