The only electrical connection in common with the three items that have failed is the earth.
Start testing with the HRW as the spade connections are easy to access and check earth and supply, could be that if the 12v is missing its not unknown.
There's NO earth connection within the tailgate so don't bother looking for it, but there's a multi point earth connection above the rear OSR tail light as shown below, the trim that houses the loudspeaker has to be detached to access it, I doubt there will be issues found there unless it's been interfered with.