Switch default tool head to extruder port #2?

Short version:
default stock tool head fails to turn extruder motor. Checked continuity along the entire length of the connection, no brake in continuity or loss of voltage along the cable. BUT we find that the extruder port #1 on the main board does NOT supply the same voltage as port #2.
So I want ask if anyone has a method to plug in the default tool head (single extruder) to the second extruder port (I’m talking about the 4-pin ports on the main board) and use that as the primary?
It sounds silly, but while Support is working with us to help resolve the issue I want to pick the brains of the community.

I believe that you would have to build a custom version of the firmware.