Linux Lite on 1 HDD, Windows 10 Pro on HDD2 not seen by Grub?

[Rapidrob]

I tried sudo update-grub but it did not see Windows 10.

[trinidad]

For MBR the first thing to do is just boot into Linux Lite and update grub. (No grub customizer) LL's default grub should detect the Windows OS on the other drive and set a chainload option entry.

For UEFI other things may be the problem and I couldn't guess without more information.

TC

[Rapidrob]

I'm running Linux Lite 4.6 on one 500 GB hard drive and a 2ND 500 GB Hard drive is running Windows 10 Pro.
I tried Grub Customizer after making sure the Win 10 Hard drive was mounted but Grub does not "see" the hard drive even if I hit "add" it does not show  up on the menu as an option.
I do not want to run the two OS's on the same hard drive unless I have to do it that way?
Are there instructions on how to run two HDD's that can be seen at boot up and selected to either to run?
Thanks for your help.