Your want your 12.04 grub in the MBR of the hard drive and the grub for 14.04 in the MBR of the SSD and set SSD as default boot in BIOS. (assumes both BIOS not UEFI).
If you used a default install both grubs may have originally installed to whichever drive is sda. And then on a major grub update will reinstall grub's boot loader to the MBR that is sda.
To see what drive grub2 uses see this line - grub-pc/install_devices:
sudo debconf-show grub-pc
sudo grub-probe -t device /boot/grub
to get grub2 to remember where to reinstall on updates:
sudo dpkg-reconfigure grub-pc
Enter thru first pages,spacebar to choose/unchoose drive, enter to accept, do not choose partitions
Then follow Elder Geek suggestion on sudo update-grub. If you run that in both installs you can boot from BIOS or one time boot key and both grub menus will show the other. There are ways to add a default boot entry to boot link to most recent kernel so you do not have to update grub in both installs on kernel updates.
https://help.ubuntu.com/community/MaintenanceFreeCustomGrub2Screen