[Retro]

I think your right Tom, on my hydraulic fan the 12v slows the fan, disconnect it and it speeds up, I think there is an electric solonoid that opens and closes a valve for the hyd fan, that gets oil pressure via the power steering.
My setup is 1995 but probably similar to this one, I would think this is operated by a temp sensor that is tied in with the ddec but not nessesarily run by it, or may have a separate senser.