[Whysguy]

I dont know what that housing is but there should be a send and return hose for coolant going to the dash heat or other heater core within the coach. My 1978 Newell had a heater core fed by the engine coolant under the bed in the rear.

This hose is separate from the two supply/return heating hoses those two hoses are easy to follow and split off to multiple heater cores & water heater
The hose I can’t follow is a thinner schedule black hose and ty wrapped with a bunch of stuff.
I can’t figure for the life of me what it could be for and coming form the V of the 903.
Hopefully someone will get me in the right direction before I go cutting more  ty wraps.