I must say, it was difficult to name this question.

Basically, I need to properly reinstall the bootloader on my system, because I already have the working system disks for my OSes.

The long story is this: I had the large slow HDD with Windows7 & Debian Wheezy dual-boot on it, perfectly bootable. Then, I ordered the SSD drive and prepared my system partitions to fit onto the much smaller SSD. I wanted the following schema:

128 GB Windows
 24 GB /     on Debian
 86 GB /home on Debian 

Strange size for /home because there's no such thing as true 256GB disk drive.

So, I've prepared such a partitions on my initial HDD and installed the new SSD and then I loaded the GParted live USB (can't remember now how it was really named), and then just copypasted the partitions from HDD to SSD.

So, now I have the following partitions across the physical disks:

SSD
   128 GB copy of original Windows partition
    24 GB copy of presumably Debian /
    86 GB copy of presumably Debian /home

HDD
   128 GB Windows
    24 GB / on Debian
    86 GB /home on Debian
    ... several other partitions with non-system data ...

And the behavior of the system right after the Ctrl+C, Ctrl+V in GParted was as follows: no GRUB, system boots right into the Windows on HDD.

In BIOS settings are to boot from SSD first.

I managed to create the Debian Testing installation USB and loaded it into the rescue mode, found that it identified my SSD as /dev/sda and installed the GRUB to the /dev/sda. Now my system loads the GRUB which lists both Windows and Debian. From HDD. So, I am now back into initial position.

Please, how I should set up the GRUB so it'll load the OSes correctly from SSD?

Should I fire up my Debian, fiddle with the GRUB's config and reinstall it again to the same place (at SSD)?