BrockSF Said:
"Time Machine Backup. How do I change my backups to a new external drive?: Will the new backup start where the old one left off. If so, how do i keep them related? Or is it as simple as just backing my whole HD with the new back up drive? Would that contain everything that my old HD has?"
-------
Using a New Hard Drive for TMB:
No. What is on your old Hard Drive, is on your old Hard Drive. Hence, they will not be related - they will not start where the old one left off.
New Hard Drive:
Use a an external Hard Drive that Is 3 times the Total Storage Capacity as that of your internal Hard Drive, if you want to keep making whole backups. Use Disk Utilities to format the Hard Drive. In it, you'd completely erase it, format it as APFS. and then use the Hard Drive for Time Machine Backups, from then on out. Store it in a safe location that only you are aware of, and only you have access to.