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You can now try using the Mac Startup Manger to boot Windows. Also, you can use the Mac Startup Manager to boot rEFInd on the flash driven and then try booting Windows from the HDD by selecting the appropriate icon on the rEFInd menu. If using rEFInd works, then we can discuss installing rEFInd to one of the internal drives.

You can now try using the Mac Startup Manger to boot Windows. Also, you can use the Mac Startup Manager to boot rEFInd on the flash driven and then try booting Windows from the HDD by selecting the appropriate icon on the rEFInd menu. Since BIOS booting Windows files have now been installed on multiple drives, you may have difficulty determining which icon represents the internal HDD. If using rEFInd works, then we can discuss installing rEFInd to one of the internal drives.

Update 4

Apparently, you can get Windows to BIOS boot from the SSD, but for some reason the Windows software installed on the SSD can not execute the winload.exe file stored on the HDD. I tested this arrangement using a virtual machine and did not have any problems booting. The only difference between the virtual machine and your Mac is your HDD is drive E: and the HDD in the virtual machines is drive D:. I can not explain why your Mac is not using drive D: for the HDD or if drive D: is being used for something else. (Update 3 did ask of the output from echo list volume | diskpart, which was never posted.)

My remaining thought would be to install the Windows boot files on the HDD and see if the Mac Boot Manager or the rEFInd Boot Manager can successfully boot Windows from the new arrangement.

You could UEFI boot from the Windows installer on the flash drive and enter the command below to get the drive letter for the Windows partition on the HDD.

echo list volume | diskpart

Here, I will assume the Windows partition on the HDD is drive E:. The following commands will write the boot files to the HDD.

bootsect /nt60 E: /mbr
bcdboot E:\windows /l en-us /s E: /f bios

You can now try using the Mac Startup Manger to boot Windows. Also, you can use the Mac Startup Manager to boot rEFInd on the flash driven and then try booting Windows from the HDD by selecting the appropriate icon on the rEFInd menu. If using rEFInd works, then we can discuss installing rEFInd to one of the internal drives.

Update 3

I would be asking the following questions.

• Does /Windows/System32/winload.exe exist in the third MBR partition on the HDD?
• Is this the location specified in the /boot/BCD file?

The /boot/BCD file is suppose to be located in the System Reserve. The System Reserve is suppose to be located in the third MBR partition on the SSD. Note: Many of the files and directories in the System Reserve have the hidden attribute. You could UEFI boot from the Windows installer on the flash drive and enter the command below to get the drive letters for the partitions in the SDD and HDD.

echo list volume | diskpart

Here, I will assume the System Reserve partition on the SSD is drive C: and the Windows partition on the HDD is drive D:.

You could then enter the command below to see if winload.exe exists.

dir D:\Windows\System32\winload.exe

You could also enter the command below to show the contents of the BCD file.

bcdedit /store C:\boot\BCD /enum

See if you can post the output from these commands.