Did you keep the control module? If so, you may or may not need the wiring harness but I'm guessing that Tiffin provided wiring to the area under the dash that leads to the connection plug at the rear of the coach. Maybe a Tiffin owner can help you out as to where the wiring harness might actually be located (my guess would be somewhere around the brake treadle under the dash) if there is one at all.
If you didn't keep the control module, I'm not sure if you'll be able to find one to purchase or not. You may be able to find a used one on ebay or somewhere else. Check THIS VENDOR
to see if they still stock the part #TC-6000K --it appears they do but I find that odd.
Even though U.S. Gear no longer makes the original system, they have kept the website up that also includes a page to access all their installation instructions and operating guides, etc. ...go HERE