I posted yesterday about my stereo not working after adding in an aux cable. I have checked what I believe to be the correct fuses (although the diagrams are inconsistent online so I'm not sure) and they seem to be fine. I am still able to use my steering wheel controls to connect my phone and I can access my contacts and calls as normal so I assume I haven't broken anything there and that the head unit just isn't getting power, but all of the ISO pins seem to be intact. I can't think what else could be wrong and I don't have a tester to find out if power is arriving at the head unit. Can anyone recommend any further troubleshooting?

Update: my odometer is flashing so it's a possible canbus issue. Will disconnecting the battery for a while solve the issue?