I know this is an old thread but i figured i would post a response. I am a technician with 20 years experience on mack/volvo trucks mostly CXN/CXU macks and VNL volvos. The issue is a shared ground between the right mirror/window/door lock circuits. Our fix to this issue is splicing into the window switch ground wire behind the dash switch and running it up to the ground stud at buss bar near fuse panel under cb radio mount. This will provide the circuit with a good ground and should fix your issue.
