You have probably found a resolution to the issue you posted about with your Thor Residency 3505. I am writing anyway, because we have a 1994 Thor Residency 3500 that I think from information I have might have the same floorplan as your 3505. We purchased our Residency from the original owner and all the records including the owner's manual came with it.
For anyone else who finds this topic, our converter is located under the entry steps.
We would be happy to share the information we have with other Residency owners. We love our Thor enough that we are updating everything, inside and out, to bring it into the 21st century.
Steve & Greta