I don't know if Volvo has changed the design, but on a friends boat, the control unit had 2 identical plugs (out of 3 total). Unfortunately, they were poorly identified and it was possible to easily mix them up. Worse, mixing them fried the unit. Even worse, it was a "Volvo certified" mechanic
that did so, but refused to acknowledge the $1000 error.
So ... before you start, carefully and properly ID each and every connection and label same in an unambiguous manner.
By the way, the actual problem proved to be a failed splice in the electrical cable between the engine box and the control head
at the helm