Dual boot Win/Lin on separate HDs with a switch - bypass Grub?

[m654321]

Just to clarify - nothing was damaged as far as Grub.  If I Switch both HDs ON then it boots to Grub, I choose an OS, and it boots fine.

Okay, sorry I misunderstood - I thought your Window's bootloader & Grub needed repairing, following on from DeepThought's comment.

My goal is to: (before the computer is turned on)  Choose the current OS by switching that HD ON and leaving the other off.  Then have the computer boot to the OS that is turned ON.

I'm not familiar at all with a hard drive switcher - I assumed you meant choosing the HDD drive from the PC's boot settings. What advantage does it confer, over the usual method of choosing your OS from the onscreen grublist when booting. TC mentions that a hard drive switcher & Grub are incompatible & gives reasons, so maybe better to drop the HDD-switcher as it just seems to over-complicate things ...

Are there settings in "Grub Customizer" that might allow this?  Or maybe a fresh install of Linux with the other HD turned off?

I would stay away from that app - my experience of it in the past is that it's pretty buggy and can really mess up things - I don't use it anymore.