Would there be a smoking gun that would cause there to be 11 volts in the cab but 12+ at the battery? It appears the fusible links have been upgraded

 

What year?

 

A bad connection. Either a corroded connection or a loose connection somewhere.

 

I wish i could help, i'm trying to find missing voltage in a 91 D350... this wiring is a ****-show... even a replacement harness seems to do the same things.

Best advice for any electrical is to clean your grounds and make sure that you use dielectric grease on connections.