You can see my disconnect switches creates a line gap on the HVAC equipment they attaches to. Is there something I can change to make it transparent?
Or can I do wireframe selectively? Just the HVAC on wireframe view?
The source of this behavior is under Mechanical Settings » Hidden Line. You can either disable "Draw MEP Hidden Lines" or set the gap sizes to 0.
The above is a Project-wide effect, though. You can eliminate this per View by setting the Visual Style to Wireframe, but you cannot assign a Visual Style to a specific Category. You could also change the View's Discipline to Coordination to prevent Revit from creating these gaps.
In this particular view, you could turn your Mechanical Equipment to transparent, that may clear up some of the issues.