Yes, that would be a true serial connection, which can be done. In trailer brake world, there aren’t any real standards that everyone goes by. it’s always been a “that’s good enough” scenario.Ya'll have me worried with warnings of series wired so I need to know how someone could make that mistake. I realize there are multiple ways of bringing + and - to each mag but in simple terms the + wire would go from 7 way to + wire on first mag,the - wire on first mag would run to + wire on secound mag,- wire on secound mag would run to + wire on third mag ect ,ect until - wire on last mag runs to - wire on 7 way. Is that how you are saying someone would wire brakes in series or is there other less obvious ways it might be wired in series? I ask because if it looks right to the one who did it,it might also look right to me. I suspect the fist voltage test would send up a flag but I'm asking for the guy doing a visual inspection for broke,disconnected or missing wires.
There should be 2 wires running from the brake controller truck/trailer plug. A hot 12+ gauge (blue is often used) and a 12+ guage ground (white is usually used). One side of the magnet goes to blue, one side to white without grounding to the frame allowing for the best current path through the controller. Some deutsch type connectors would probably help but they cost about 4 bucks each.
People tend to ”ground out” the individual drums often using zip screws into the frame breaking the path. They tend to use clamp on splices or crimp on splices without heat shrink. Over time, corroding and contributing to an increase in line resistance. With current being reduced by resistance (current=voltage/resistance) the goal is to minimize resistance since voltage is the constant we need for the controller to do its job.