You have El Capitan, so we need to disable SIP.
1. Boot into Local Recovery (Command+R).
2. Start Utilities -> Terminal.
3. Type csrutil disable in Terminal and press Enter/Return.
4. Type csrutil status.
5. Boot normally, and type csrutil status to confirm that all individual entries are still disabled.
You need to run this on disk0 (1TB SSD) not on disk1 (old 500GB HDD). Confirm with diskutil list and pick the correct disk. Modify the following step 1, as appropriate.
Rebuild MBR to match the new GPT information thus resetting the Hybrid MBR. Use defaults for other questions (like partition codes). The only values that need modifications are the Boot flags and step 10. Accept all other defaults that Gdisk offers. Please see thesample Q&A as an example. These steps can be repeated if you make a mistake before you get to Step 12, otherwise start from Step 1 for these steps. Step 6 has numbers which are typed with a space between the numbers. Please see the sample Q&A before you execute these steps.
- Sudo gdisk /dev/rdisk0
- P (Print list of parts)
- R (Recover)
- O (print current Hybrid MBR)
- H (chooses Hybrid)
- Partitions numbers to be hybridized: 2 3 4
- Y (Good for GRUB question)
- N (part 2 boot flag)
- N (part 3 boot flag)
- Y (part 4 boot flag make NTFS bootable partition)
- O (print current Hybrid MBR)
- W (Write the new MBR)
- Y (Yes! write the new MBR)
- Reboot
Here is sample Q&A for this section. Please notice the Press Enter/Return.
Place EFI GPT (0xEE) partition first in MBR (good for GRUB)? (Y/N): Y
Creating entry for GPT partition #2 (MBR partition #2)
Enter an MBR hex code (default AF): Press Enter/Return
Set the bootable flag? (Y/N): N
Creating entry for GPT partition #3 (MBR partition #3)
Enter an MBR hex code (default AB): Press Enter/Return
Set the bootable flag? (Y/N): N
Creating entry for GPT partition #4 (MBR partition #4)
Enter an MBR hex code (default 07): Press Enter/Return
Set the bootable flag? (Y/N): Y
Test 1 - Does Bootcamp Volume show up in Finder?
Test 2 - Can you see files in Bootcamp Volume?
Test 3 - Can you select Bootcamp in System Preferences -> Startup Disk?
Test 4 - If Test 3 is successful, select Bootcamp and Click Restart.
