Welcome Thomas, the info you are looking for is located in the “Freightliner Recreational Vehicle Chassis Operator’s and Maintenance Manual”. It would have been part of the info package Winnebago provided when the vehicle was delivered. If a replacement is needed you might try EBAY.
I took a picture of the manual cover to aid in a search and the message center configuration my 2002 Horizon has, I hope this helps.
02 Itasca Horizon 36LD, Cat 3126E, Allison MD3000MH
09 Colorado Z71 Ex Cab, SMI AF1, Demco Base Plate & Tow Bar.